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The Array object, as with arrays in other programming languages, enables storing a collection of multiple items under a single variable name , and has members for performing common array operations .

Description

In JavaScript, arrays aren't primitives but are instead Array objects with the following core characteristics:

JavaScript arrays are resizable and can contain a mix of different data types . (When those characteristics are undesirable, use typed arrays instead.)
JavaScript arrays are not associative arrays and so, array elements cannot be accessed using arbitrary strings as indexes, but must be accessed using nonnegative integers (or their respective string form) as indexes.
JavaScript arrays are zero-indexed : the first element of an array is at index 0 , the second is at index 1 , and so on — and the last element is at the value of the array's length property minus 1 .
JavaScript array-copy operations create shallow copies . (All standard built-in copy operations with any JavaScript objects create shallow copies, rather than deep copies ).

Array indices

Array objects cannot use arbitrary strings as element indexes (as in an associative array ) but must use nonnegative integers (or their respective string form). Setting or accessing via non-integers will not set or retrieve an element from the array list itself, but will set or access a variable associated with that array's object property collection . The array's object properties and list of array elements are separate, and the array's traversal and mutation operations cannot be applied to these named properties.

Array elements are object properties in the same way that toString is a property (to be specific, however, toString() is a method). Nevertheless, trying to access an element of an array as follows throws a syntax error because the property name is not valid:

JavaScript syntax requires properties beginning with a digit to be accessed using bracket notation instead of dot notation . It's also possible to quote the array indices (e.g., years['2'] instead of years[2] ), although usually not necessary.

The 2 in years[2] is coerced into a string by the JavaScript engine through an implicit toString conversion. As a result, '2' and '02' would refer to two different slots on the years object, and the following example could be true :

Only years['2'] is an actual array index. years['02'] is an arbitrary string property that will not be visited in array iteration.

Relationship between length and numerical properties

A JavaScript array's length property and numerical properties are connected.

Several of the built-in array methods (e.g., join() , slice() , indexOf() , etc.) take into account the value of an array's length property when they're called.

Other methods (e.g., push() , splice() , etc.) also result in updates to an array's length property.

When setting a property on a JavaScript array when the property is a valid array index and that index is outside the current bounds of the array, the engine will update the array's length property accordingly:

Increasing the length .

Decreasing the length property does, however, delete elements.

This is explained further on the Array/length page.

Array methods and empty slots

Empty slots in sparse arrays behave inconsistently between array methods. Generally, the older methods will skip empty slots, while newer ones treat them as undefined .

Among methods that iterate through multiple elements, the following do an in check before accessing the index and do not conflate empty slots with undefined :

For exactly how they treat empty slots, see the page for each method.

These methods treat empty slots as if they are undefined :

Copying methods and mutating methods

Some methods do not mutate the existing array that the method was called on, but instead return a new array. They do so by first accessing this.constructor[Symbol.species] to determine the constructor to use for the new array. The newly constructed array is then populated with elements. The copy always happens shallowly — the method never copies anything beyond the initially created array. Elements of the original array(s) are copied into the new array as follows:

Other methods mutate the array that the method was called on, in which case their return value differs depending on the method: sometimes a reference to the same array, sometimes the length of the new array.

The following methods create new arrays with @@species :

splice() (to construct the array of removed elements that's returned)

Note that group() and groupToMap() do not use @@species to create new arrays for each group entry, but always use the plain Array constructor. Conceptually, they are not copying methods either.

The following methods mutate the original array:

Iterative methods

Many array methods take a callback function as an argument. The callback function is called sequentially and at most once for each element in the array, and the return value of the callback function is used to determine the return value of the method. They all share the same signature:

Where callbackFn takes three arguments:

The current element being processed in the array.

The index of the current element being processed in the array.

The array that the method was called upon.

What callbackFn is expected to return depends on the array method that was called.

The thisArg argument (defaults to undefined ) will be used as the this value when calling callbackFn . The this value ultimately observable by callbackFn is determined according to the usual rules : if callbackFn is non-strict , primitive this values are wrapped into objects, and undefined / null is substituted with globalThis . The thisArg argument is irrelevant for any callbackFn defined with an arrow function , as arrow functions don't have their own this binding.

All iterative methods are copying and generic , although they behave differently with empty slots .

The following methods are iterative:

groupToMap()

In particular, every() , find() , findIndex() , findLast() , findLastIndex() , and some() do not always invoke callbackFn on every element — they stop iteration as soon as the return value is determined.

There are two other methods that take a callback function and run it at most once for each element in the array, but they have slightly different signatures from typical iterative methods (for example, they don't accept thisArg ):

The sort() method also takes a callback function, but it is not an iterative method. It mutates the array in-place, doesn't accept thisArg , and may invoke the callback multiple times on an index.

Generic array methods

Array methods are always generic — they don't access any internal data of the array object. They only access the array elements through the length property and the indexed elements. This means that they can be called on array-like objects as well.

Normalization of the length property

The length property is converted to an integer and then clamped to the range between 0 and 2 53 - 1. NaN becomes 0 , so even when length is not present or is undefined , it behaves as if it has value 0 .

Some array methods set the length property of the array object. They always set the value after normalization, so length always ends as an integer.

Array-like objects

The term array-like object refers to any object that doesn't throw during the length conversion process described above. In practice, such object is expected to actually have a length property and to have indexed elements in the range 0 to length - 1 . (If it doesn't have all indices, it will be functionally equivalent to a sparse array .)

Many DOM objects are array-like — for example, NodeList and HTMLCollection . The arguments object is also array-like. You can call array methods on them even if they don't have these methods themselves.

Constructor

Creates a new Array object.

Static properties

Returns the Array constructor.

Static methods

Creates a new Array instance from an array-like object or iterable object.

Returns true if the argument is an array, or false otherwise.

Creates a new Array instance with a variable number of arguments, regardless of number or type of the arguments.

Instance properties

These properties are defined on Array.prototype and shared by all Array instances.

The constructor function that created the instance object. For Array instances, the initial value is the Array constructor.

Contains property names that were not included in the ECMAScript standard prior to the ES2015 version and that are ignored for with statement-binding purposes.

These properties are own properties of each Array instance.

Reflects the number of elements in an array.

Instance methods

Returns the array item at the given index. Accepts negative integers, which count back from the last item.

Returns a new array that is the calling array joined with other array(s) and/or value(s).

Copies a sequence of array elements within an array.

Returns a new array iterator object that contains the key/value pairs for each index in an array.

Returns true if every element in the calling array satisfies the testing function.

Fills all the elements of an array from a start index to an end index with a static value.

Returns a new array containing all elements of the calling array for which the provided filtering function returns true .

Returns the value of the first element in the array that satisfies the provided testing function, or undefined if no appropriate element is found.

Returns the index of the first element in the array that satisfies the provided testing function, or -1 if no appropriate element was found.

Returns the value of the last element in the array that satisfies the provided testing function, or undefined if no appropriate element is found.

Returns the index of the last element in the array that satisfies the provided testing function, or -1 if no appropriate element was found.

Returns a new array with all sub-array elements concatenated into it recursively up to the specified depth.

Returns a new array formed by applying a given callback function to each element of the calling array, and then flattening the result by one level.

Calls a function for each element in the calling array.

Groups the elements of an array into an object according to the strings returned by a test function.

Groups the elements of an array into a Map according to values returned by a test function.

Determines whether the calling array contains a value, returning true or false as appropriate.

Returns the first (least) index at which a given element can be found in the calling array.

Joins all elements of an array into a string.

Returns a new array iterator that contains the keys for each index in the calling array.

Returns the last (greatest) index at which a given element can be found in the calling array, or -1 if none is found.

Returns a new array containing the results of invoking a function on every element in the calling array.

Removes the last element from an array and returns that element.

Adds one or more elements to the end of an array, and returns the new length of the array.

Executes a user-supplied "reducer" callback function on each element of the array (from left to right), to reduce it to a single value.

Executes a user-supplied "reducer" callback function on each element of the array (from right to left), to reduce it to a single value.

Reverses the order of the elements of an array in place . (First becomes the last, last becomes first.)

Removes the first element from an array and returns that element.

Extracts a section of the calling array and returns a new array.

Returns true if at least one element in the calling array satisfies the provided testing function.

Sorts the elements of an array in place and returns the array.

Adds and/or removes elements from an array.

Returns a localized string representing the calling array and its elements. Overrides the Object.prototype.toLocaleString() method.

Returns a string representing the calling array and its elements. Overrides the Object.prototype.toString() method.

Adds one or more elements to the front of an array, and returns the new length of the array.

Returns a new array iterator object that contains the values for each index in the array.

An alias for the values() method by default.

This section provides some examples of common array operations in JavaScript.

Note: If you're not yet familiar with array basics, consider first reading JavaScript First Steps: Arrays , which explains what arrays are , and includes other examples of common array operations.

Create an array

This example shows three ways to create new array: first using array literal notation , then using the Array() constructor, and finally using String.prototype.split() to build the array from a string.

Create a string from an array

This example uses the join() method to create a string from the fruits array.

Access an array item by its index

This example shows how to access items in the fruits array by specifying the index number of their position in the array.

Find the index of an item in an array

This example uses the indexOf() method to find the position (index) of the string "Banana" in the fruits array.

Check if an array contains a certain item

This example shows two ways to check if the fruits array contains "Banana" and "Cherry" : first with the includes() method, and then with the indexOf() method to test for an index value that's not -1 .

Append an item to an array

This example uses the push() method to append a new string to the fruits array.

Remove the last item from an array

This example uses the pop() method to remove the last item from the fruits array.

Note: pop() can only be used to remove the last item from an array. To remove multiple items from the end of an array, see the next example.

Remove multiple items from the end of an array

This example uses the splice() method to remove the last 3 items from the fruits array.

Truncate an array down to just its first N items

This example uses the splice() method to truncate the fruits array down to just its first 2 items.

Remove the first item from an array

This example uses the shift() method to remove the first item from the fruits array.

Note: shift() can only be used to remove the first item from an array. To remove multiple items from the beginning of an array, see the next example.

Remove multiple items from the beginning of an array

This example uses the splice() method to remove the first 3 items from the fruits array.

Add a new first item to an array

This example uses the unshift() method to add, at index 0 , a new item to the fruits array — making it the new first item in the array.

Remove a single item by index

This example uses the splice() method to remove the string "Banana" from the fruits array — by specifying the index position of "Banana" .

Remove multiple items by index

This example uses the splice() method to remove the strings "Banana" and "Strawberry" from the fruits array — by specifying the index position of "Banana" , along with a count of the number of total items to remove.

Replace multiple items in an array

This example uses the splice() method to replace the last 2 items in the fruits array with new items.

Iterate over an array

This example uses a for...of loop to iterate over the fruits array, logging each item to the console.

But for...of is just one of many ways to iterate over any array; for more ways, see Loops and iteration , and see the documentation for the every() , filter() , flatMap() , map() , reduce() , and reduceRight() methods — and see the next example, which uses the forEach() method.

Call a function on each element in an array

This example uses the forEach() method to call a function on each element in the fruits array; the function causes each item to be logged to the console, along with the item's index number.

Merge multiple arrays together

This example uses the concat() method to merge the fruits array with a moreFruits array, to produce a new combinedFruits array. Notice that fruits and moreFruits remain unchanged.

Copy an array

This example shows three ways to create a new array from the existing fruits array: first by using spread syntax , then by using the from() method, and then by using the slice() method.

All built-in array-copy operations ( spread syntax , Array.from() , Array.prototype.slice() , and Array.prototype.concat() ) create shallow copies . If you instead want a deep copy of an array, you can use JSON.stringify() to convert the array to a JSON string, and then JSON.parse() to convert the string back into a new array that's completely independent from the original array.

You can also create deep copies using the structuredClone() method, which has the advantage of allowing transferable objects in the source to be transferred to the new copy, rather than just cloned.

Finally, it's important to understand that assigning an existing array to a new variable doesn't create a copy of either the array or its elements. Instead the new variable is just a reference, or alias, to the original array; that is, the original array's name and the new variable name are just two names for the exact same object (and so will always evaluate as strictly equivalent ). Therefore, if you make any changes at all either to the value of the original array or to the value of the new variable, the other will change, too:

Grouping the elements of an array

The Array.prototype.group() methods can be used to group the elements of an array, using a test function that returns a string indicating the group of the current element.

Here we have a simple inventory array that contains "food" objects that have a name and a type .

To use group() , you supply a callback function that is called with the current element, and optionally the current index and array, and returns a string indicating the group of the element.

The code below uses an arrow function to return the type of each array element (this uses object destructuring syntax for function arguments to unpack the type element from the passed object). The result is an object that has properties named after the unique strings returned by the callback. Each property is assigned an array containing the elements in the group.

Note that the returned object references the same elements as the original array (not deep copies ). Changing the internal structure of these elements will be reflected in both the original array and the returned object.

If you can't use a string as the key, for example, if the information to group is associated with an object that might change, then you can instead use Array.prototype.groupToMap() . This is very similar to group except that it groups the elements of the array into a Map that can use an arbitrary value ( object or primitive ) as a key.

Creating a two-dimensional array

The following creates a chessboard as a two-dimensional array of strings. The first move is made by copying the 'p' in board[6][4] to board[4][4] . The old position at [6][4] is made blank.

Here is the output:

Using an array to tabulate a set of values

Creating an array using the result of a match.

The result of a match between a RegExp and a string can create a JavaScript array that has properties and elements which provide information about the match. Such an array is returned by RegExp.prototype.exec() and String.prototype.match() .

For more information about the result of a match, see the RegExp.prototype.exec() and String.prototype.match() pages.

Specifications

Browser compatibility.

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An array is a special variable, which can hold more than one value:

Why Use Arrays?

If you have a list of items (a list of car names, for example), storing the cars in single variables could look like this:

However, what if you want to loop through the cars and find a specific one? And what if you had not 3 cars, but 300?

The solution is an array!

An array can hold many values under a single name, and you can access the values by referring to an index number.

Creating an Array

Using an array literal is the easiest way to create a JavaScript Array.

It is a common practice to declare arrays with the const keyword.

Learn more about const with arrays in the chapter: JS Array Const .

Spaces and line breaks are not important. A declaration can span multiple lines:

You can also create an array, and then provide the elements:

Using the JavaScript Keyword new

The following example also creates an Array, and assigns values to it:

The two examples above do exactly the same.

There is no need to use new Array() .

For simplicity, readability and execution speed, use the array literal method.

Accessing Array Elements

You access an array element by referring to the index number :

Note: Array indexes start with 0.

[0] is the first element. [1] is the second element.

Changing an Array Element

This statement changes the value of the first element in cars :

Access the Full Array

With JavaScript, the full array can be accessed by referring to the array name:

Arrays are Objects

Arrays are a special type of objects. The typeof operator in JavaScript returns "object" for arrays.

But, JavaScript arrays are best described as arrays.

Arrays use numbers to access its "elements". In this example, person[0] returns John:

Objects use names to access its "members". In this example, person.firstName returns John:

Array Elements Can Be Objects

JavaScript variables can be objects. Arrays are special kinds of objects.

Because of this, you can have variables of different types in the same Array.

You can have objects in an Array. You can have functions in an Array. You can have arrays in an Array:

Array Properties and Methods

The real strength of JavaScript arrays are the built-in array properties and methods:

Array methods are covered in the next chapters.

The length Property

The length property of an array returns the length of an array (the number of array elements).

The length property is always one more than the highest array index.

Accessing the First Array Element

Accessing the last array element, looping array elements.

One way to loop through an array, is using a for loop:

You can also use the Array.forEach() function:

Adding Array Elements

The easiest way to add a new element to an array is using the push() method:

New element can also be added to an array using the length property:

Adding elements with high indexes can create undefined "holes" in an array:

Associative Arrays

Many programming languages support arrays with named indexes.

Arrays with named indexes are called associative arrays (or hashes).

JavaScript does not support arrays with named indexes.

In JavaScript, arrays always use numbered indexes .

WARNING !! If you use named indexes, JavaScript will redefine the array to an object.

After that, some array methods and properties will produce incorrect results .

Example:

The difference between arrays and objects.

In JavaScript, arrays use numbered indexes .

In JavaScript, objects use named indexes .

Arrays are a special kind of objects, with numbered indexes.

When to Use Arrays. When to use Objects.

JavaScript new Array()

JavaScript has a built-in array constructor new Array() .

But you can safely use [] instead.

These two different statements both create a new empty array named points:

These two different statements both create a new array containing 6 numbers:

The new keyword can produce some unexpected results:

A Common Error

is not the same as:

How to Recognize an Array

A common question is: How do I know if a variable is an array?

The problem is that the JavaScript operator typeof returns " object ":

The typeof operator returns object because a JavaScript array is an object.

Solution 1:

To solve this problem ECMAScript 5 (JavaScript 2009) defined a new method Array.isArray() :

Solution 2:

The instanceof operator returns true if an object is created by a given constructor:

Complete Array Reference

For a complete Array reference, go to our:

Complete JavaScript Array Reference .

The reference contains descriptions and examples of all Array properties and methods.

Test Yourself With Exercises

Get the value " Volvo " from the cars array.

Start the Exercise

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The JavaScript language

Destructuring assignment

The two most used data structures in JavaScript are Object and Array .

Although, when we pass those to a function, it may need not be an object/array as a whole. It may need individual pieces.

Destructuring assignment is a special syntax that allows us to “unpack” arrays or objects into a bunch of variables, as sometimes that’s more convenient.

Destructuring also works great with complex functions that have a lot of parameters, default values, and so on. Soon we’ll see that.

Array destructuring

Here’s an example of how an array is destructured into variables:

Now we can work with variables instead of array members.

It looks great when combined with split or other array-returning methods:

As you can see, the syntax is simple. There are several peculiar details though. Let’s see more examples, to better understand it.

It’s called “destructuring assignment,” because it “destructurizes” by copying items into variables. But the array itself is not modified.

It’s just a shorter way to write:

Unwanted elements of the array can also be thrown away via an extra comma:

In the code above, the second element of the array is skipped, the third one is assigned to title , and the rest of the array items is also skipped (as there are no variables for them).

…Actually, we can use it with any iterable, not only arrays:

That works, because internally a destructuring assignment works by iterating over the right value. It’s a kind of syntax sugar for calling for..of over the value to the right of = and assigning the values.

We can use any “assignables” on the left side.

For instance, an object property:

In the previous chapter we saw the Object.entries(obj) method.

We can use it with destructuring to loop over keys-and-values of an object:

The similar code for a Map is simpler, as it’s iterable:

There’s a well-known trick for swapping values of two variables using a destructuring assignment:

Here we create a temporary array of two variables and immediately destructure it in swapped order.

We can swap more than two variables this way.

The rest ‘…’

Usually, if the array is longer than the list at the left, the “extra” items are omitted.

For example, here only two items are taken, and the rest is just ignored:

If we’d like also to gather all that follows – we can add one more parameter that gets “the rest” using three dots "..." :

The value of rest is the array of the remaining array elements.

We can use any other variable name in place of rest , just make sure it has three dots before it and goes last in the destructuring assignment.

Default values

If the array is shorter than the list of variables at the left, there’ll be no errors. Absent values are considered undefined:

If we want a “default” value to replace the missing one, we can provide it using = :

Default values can be more complex expressions or even function calls. They are evaluated only if the value is not provided.

For instance, here we use the prompt function for two defaults:

Please note: the prompt will run only for the missing value ( surname ).

Object destructuring

The destructuring assignment also works with objects.

The basic syntax is:

We should have an existing object on the right side, that we want to split into variables. The left side contains an object-like “pattern” for corresponding properties. In the simplest case, that’s a list of variable names in {...} .

Properties options.title , options.width and options.height are assigned to the corresponding variables.

The order does not matter. This works too:

The pattern on the left side may be more complex and specify the mapping between properties and variables.

If we want to assign a property to a variable with another name, for instance, make options.width go into the variable named w , then we can set the variable name using a colon:

The colon shows “what : goes where”. In the example above the property width goes to w , property height goes to h , and title is assigned to the same name.

For potentially missing properties we can set default values using "=" , like this:

Just like with arrays or function parameters, default values can be any expressions or even function calls. They will be evaluated if the value is not provided.

In the code below prompt asks for width , but not for title :

We also can combine both the colon and equality:

If we have a complex object with many properties, we can extract only what we need:

The rest pattern “…”

What if the object has more properties than we have variables? Can we take some and then assign the “rest” somewhere?

We can use the rest pattern, just like we did with arrays. It’s not supported by some older browsers (IE, use Babel to polyfill it), but works in modern ones.

It looks like this:

In the examples above variables were declared right in the assignment: let {…} = {…} . Of course, we could use existing variables too, without let . But there’s a catch.

This won’t work:

The problem is that JavaScript treats {...} in the main code flow (not inside another expression) as a code block. Such code blocks can be used to group statements, like this:

So here JavaScript assumes that we have a code block, that’s why there’s an error. We want destructuring instead.

To show JavaScript that it’s not a code block, we can wrap the expression in parentheses (...) :

Nested destructuring

If an object or an array contain other nested objects and arrays, we can use more complex left-side patterns to extract deeper portions.

In the code below options has another object in the property size and an array in the property items . The pattern on the left side of the assignment has the same structure to extract values from them:

All properties of options object except extra that is absent in the left part, are assigned to corresponding variables:

Finally, we have width , height , item1 , item2 and title from the default value.

Note that there are no variables for size and items , as we take their content instead.

Smart function parameters

There are times when a function has many parameters, most of which are optional. That’s especially true for user interfaces. Imagine a function that creates a menu. It may have a width, a height, a title, items list and so on.

Here’s a bad way to write such function:

In real-life, the problem is how to remember the order of arguments. Usually IDEs try to help us, especially if the code is well-documented, but still… Another problem is how to call a function when most parameters are ok by default.

That’s ugly. And becomes unreadable when we deal with more parameters.

Destructuring comes to the rescue!

We can pass parameters as an object, and the function immediately destructurizes them into variables:

We can also use more complex destructuring with nested objects and colon mappings:

The full syntax is the same as for a destructuring assignment:

Then, for an object of parameters, there will be a variable varName for property incomingProperty , with defaultValue by default.

Please note that such destructuring assumes that showMenu() does have an argument. If we want all values by default, then we should specify an empty object:

We can fix this by making {} the default value for the whole object of parameters:

In the code above, the whole arguments object is {} by default, so there’s always something to destructurize.

Destructuring assignment allows for instantly mapping an object or array onto many variables.

The full object syntax:

This means that property prop should go into the variable varName and, if no such property exists, then the default value should be used.

Object properties that have no mapping are copied to the rest object.

The full array syntax:

The first item goes to item1 ; the second goes into item2 , all the rest makes the array rest .

It’s possible to extract data from nested arrays/objects, for that the left side must have the same structure as the right one.

We have an object:

Write the destructuring assignment that reads:

Here’s an example of the values after your assignment:

The maximal salary

There is a salaries object:

Create the function topSalary(salaries) that returns the name of the top-paid person.

P.S. Use Object.entries and destructuring to iterate over key/value pairs.

Open a sandbox with tests.

Open the solution with tests in a sandbox.

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JavaScript Multidimensional Array

JavaScript Arrays

In this tutorial, you will learn about JavaScript arrays with the help of examples.

An array is an object that can store multiple values at once. For example,

Here, words is an array. The array is storing 3 values.

Create an Array

You can create an array using two ways:

1. Using an array literal

The easiest way to create an array is by using an array literal [] . For example,

2. Using the new keyword

You can also create an array using JavaScript's new keyword.

In both of the above examples, we have created an array having two elements.

Note : It is recommended to use array literal to create an array.

Here are more examples of arrays:

You can also store arrays, functions and other objects inside an array. For example,

Access Elements of an Array

You can access elements of an array using indices (0, 1, 2 …) . For example,

Array indexing in JavaScript

Note : Array's index starts with 0, not 1.

Add an Element to an Array

You can use the built-in method push() and unshift() to add elements to an array.

The push() method adds an element at the end of the array. For example,

The unshift() method adds an element at the beginning of the array. For example,

Change the Elements of an Array

You can also add elements or change the elements by accessing the index value.

Suppose, an array has two elements. If you try to add an element at index 3 (fourth element), the third element will be undefined. For example,

Basically, if you try to add elements to high indices, the indices in between will have undefined value.

Remove an Element from an Array

You can use the pop() method to remove the last element from an array. The pop() method also returns the returned value. For example,

If you need to remove the first element, you can use the shift() method. The shift() method removes the first element and also returns the removed element. For example,

Array length

You can find the length of an element (the number of elements in an array) using the length property. For example,

Array Methods

In JavaScript, there are various array methods available that makes it easier to perform useful calculations.

Some of the commonly used JavaScript array methods are:

Example: JavaScript Array Methods

Note : If the element is not in an array, indexOf() gives -1.

Visit JavaScript Array Methods to learn more.

Working of JavaScript Arrays

In JavaScript, an array is an object. And, the indices of arrays are objects keys.

Since arrays are objects, the array elements are stored by reference. Hence, when an array value is copied, any change in the copied array will also reflect in the original array. For example,

You can also store values by passing a named key in an array. For example,

Array indexing in JavaScript

However, it is not recommended to store values by passing arbitrary names in an array.

Hence in JavaScript, you should use an array if values are in ordered collection. Otherwise it's better to use object with { } .

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JavaScript array - Exercises, Practice, Solution

Javascript array [53 exercises with solution].

1. Write a JavaScript function to check whether an `input` is an array or not. Go to the editor Test Data : console.log(is_array('w3resource')); console.log(is_array([1, 2, 4, 0])); false true Click me to see the solution

2. Write a JavaScript function to clone an array. Go to the editor Test Data : console.log(array_Clone([1, 2, 4, 0])); console.log(array_Clone([1, 2, [4, 0]])); [1, 2, 4, 0] [1, 2, [4, 0]] Click me to see the solution

3. Write a JavaScript function to get the first element of an array. Passing a parameter 'n' will return the first 'n' elements of the array. Go to the editor Test Data : console.log(first([7, 9, 0, -2])); console.log(first([],3)); console.log(first([7, 9, 0, -2],3)); console.log(first([7, 9, 0, -2],6)); console.log(first([7, 9, 0, -2],-3)); Expected Output : 7 [] [7, 9, 0] [7, 9, 0, -2] [] Click me to see the solution

4. Write a JavaScript function to get the last element of an array. Passing a parameter 'n' will return the last 'n' elements of the array. Go to the editor Test Data : console.log(last([7, 9, 0, -2])); console.log(last([7, 9, 0, -2],3)); console.log(last([7, 9, 0, -2],6)); Expected Output : -2 [9, 0, -2] [7, 9, 0, -2] Click me to see the solution

5. Write a simple JavaScript program to join all elements of the following array into a string. Go to the editor Sample array : myColor = ["Red", "Green", "White", "Black"]; Expected Output : "Red,Green,White,Black" "Red,Green,White,Black" "Red+Green+White+Black" Click me to see the solution

6. Write a JavaScript program which accept a number as input and insert dashes (-) between each two even numbers. For example if you accept 025468 the output should be 0-254-6-8. Go to the editor Click me to see the solution

7. Write a JavaScript program to sort the items of an array. Go to the editor Sample array : var arr1 = [ -3, 8, 7, 6, 5, -4, 3, 2, 1 ]; Sample Output : -4,-3,1,2,3,5,6,7,8 Click me to see the solution 8. Write a JavaScript program to find the most frequent item of an array. Go to the editor Sample array : var arr1=[3, 'a', 'a', 'a', 2, 3, 'a', 3, 'a', 2, 4, 9, 3]; Sample Output : a ( 5 times ) Click me to see the solution

9. Write a JavaScript program which accept a string as input and swap the case of each character. For example if you input 'The Quick Brown Fox' the output should be 'tHE qUICK bROWN fOX'. Go to the editor Click me to see the solution

10. Write a JavaScript program which prints the elements of the following array. Go to the editor Note : Use nested for loops. Sample array : var a = [[1, 2, 1, 24], [8, 11, 9, 4], [7, 0, 7, 27], [7, 4, 28, 14], [3, 10, 26, 7]]; Sample Output : "row 0" " 1" " 2" " 1" " 24" "row 1" ------ ------ Click me to see the solution

11. Write a JavaScript program to find the sum of squares of a numeric vector. Go to the editor Click me to see the solution

12. Write a JavaScript program to compute the sum and product of an array of integers. Go to the editor Click me to see the solution

add elements in an blank array

14. Write a JavaScript program to remove duplicate items from an array (ignore case sensitivity). Go to the editor Click me to see the solution

15. We have the following arrays : Go to the editor color = ["Blue ", "Green", "Red", "Orange", "Violet", "Indigo", "Yellow "]; o = ["th","st","nd","rd"] Write a JavaScript program to display the colors in the following way : "1st choice is Blue ." "2nd choice is Green." "3rd choice is Red." - - - - - - - - - - - - - Note : Use ordinal numbers to tell their position. Click me to see the solution

16. Write a JavaScript program to find the leap years in a given range of years. Go to the editor Click me to see the solution

17. Write a JavaScript program to shuffle an array. Go to the editor Click me to see the solution

18. Write a JavaScript program to perform a binary search. Go to the editor Note : A binary search or half-interval search algorithm finds the position of a specified input value within an array sorted by key value. Sample array : var items = [1, 2, 3, 4, 5, 7, 8, 9]; Expected Output : console.log(binary_Search(items, 1)); //0 console.log(binary_Search(items, 5)); //4 Click me to see the solution

19. There are two arrays with individual values, write a JavaScript program to compute the sum of each individual index value from the given arrays. Go to the editor Sample array : array1 = [1,0,2,3,4]; array2 = [3,5,6,7,8,13]; Expected Output : [4, 5, 8, 10, 12, 13] Click me to see the solution

20. Write a JavaScript program to find duplicate values in a JavaScript array. Go to the editor Click me to see the solution

21. Write a JavaScript program to flatten a nested (any depth) array. If you pass shallow, the array will only be flattened a single level. Go to the editor Sample Data : console.log(flatten([1, [2], [3, [[4]]],[5,6]])); [1, 2, 3, 4, 5, 6] console.log(flatten([1, [2], [3, [[4]]],[5,6]], true)); [1, 2, 3, [[4]], 5, 6] Click me to see the solution

22. Write a JavaScript program to compute the union of two arrays. Go to the editor Sample Data : console.log(union([1, 2, 3], [100, 2, 1, 10])); [1, 2, 3, 10, 100] Click me to see the solution

23. Write a JavaScript function to find the difference of two arrays. Go to the editor Test Data : console.log(difference([1, 2, 3], [100, 2, 1, 10])); ["3", "10", "100"] console.log(difference([1, 2, 3, 4, 5], [1, [2], [3, [[4]]],[5,6]])); ["6"] console.log(difference([1, 2, 3], [100, 2, 1, 10])); ["3", "10", "100"] Click me to see the solution

24. Write a JavaScript function to remove. 'null', '0', '""', 'false', 'undefined' and 'NaN' values from an array. Go to the editor Sample array : [NaN, 0, 15, false, -22, '',undefined, 47, null] Expected result : [15, -22, 47] Click me to see the solution

25. Write a JavaScript function to sort the following array of objects by title value. Go to the editor Sample object :

Expected result :

Click me to see the solution

26. Write a JavaScript program to find a pair of elements (indices of the two numbers) from an given array whose sum equals a specific target number. Go to the editor

Input: numbers= [10,20,10,40,50,60,70], target=50 Output: 2, 3

27. Write a JavaScript function to retrieve the value of a given property from all elements in an array. Go to the editor Sample array : [NaN, 0, 15, false, -22, '',undefined, 47, null] Expected result : [15, -22, 47] Click me to see the solution

28. Write a JavaScript function to find the longest common starting substring in a set of strings. Go to the editor

Sample array : console.log(longest_common_starting_substring(['go', 'google'])); Expected result : "go"

29. Write a JavaScript function to fill an array with values (numeric, string with one character) on supplied bounds. Go to the editor

Test Data : console.log(num_string_range('a', "z", 2)); ["a", "c", "e", "g", "i", "k", "m", "o", "q", "s", "u", "w", "y"]

30. Write a JavaScript function to merge two arrays and removes all duplicates elements. Go to the editor

Test data : var array1 = [1, 2, 3]; var array2 = [2, 30, 1]; console.log(merge_array(array1, array2)); [3, 2, 30, 1]

31. Write a JavaScript function to remove a specific element from an array. Go to the editor

Test data : console.log(remove_array_element([2, 5, 9, 6], 5)); [2, 9, 6] Click me to see the solution

32. Write a JavaScript function to find an array contains a specific element. Go to the editor

Test data : arr = [2, 5, 9, 6]; console.log(contains(arr, 5)); [True] Click me to see the solution

33. Write a JavaScript script to empty an array keeping the original. Go to the editor

Click me to see the solution .

34. Write a JavaScript function to get nth largest element from an unsorted array. Go to the editor

Test Data : console.log(nthlargest([ 43, 56, 23, 89, 88, 90, 99, 652], 4)); 89

35. Write a JavaScript function to get a random item from an array. Go to the editor

36. Write a JavaScript function to create a specified number of elements with pre-filled numeric value array. Go to the editor

Test Data : console.log(array_filled(6, 0)); [0, 0, 0, 0, 0, 0] console.log(array_filled(4, 11)); [11, 11, 11, 11]

37. Write a JavaScript function to create a specified number of elements with pre-filled string value array. Go to the editor

Test Data : console.log(array_filled(3, 'default value')); ["default value", "default value", "default value"] console.log(array_filled(4, 'password')); ["password", "password", "password", "password"] Click me to see the solution

38. Write a JavaScript function to move an array element from one position to another. Go to the editor

Test Data : console.log(move([10, 20, 30, 40, 50], 0, 2)); [20, 30, 10, 40, 50] console.log(move([10, 20, 30, 40, 50], -1, -2)); [10, 20, 30, 50, 40] Click me to see the solution

39. Write a JavaScript function to filter false, null, 0 and blank values from an array. Go to the editor

Test Data : console.log(filter_array_values([58, '', 'abcd', true, null, false, 0])); [58, "abcd", true] Click me to see the solution

40. Write a JavaScript function to generate an array of specified length, filled with integer numbers, increase by one from starting position. Go to the editor

Test Data : console.log(array_range(1, 4)); [1, 2, 3, 4] console.log(array_range(-6, 4)); [-6, -5, -4, -3] Click me to see the solution

41. Write a JavaScript function to generate an array between two integers of 1 step length. Go to the editor

Test Data : console.log(rangeBetwee(4, 7)); [4, 5, 6, 7] console.log(rangeBetwee(-4, 7)); [-4, -3, -2, -1, 0, 1, 2, 3, 4, 5, 6, 7] Click me to see the solution

42. Write a JavaScript function to find the unique elements from two arrays. Go to the editor

Test Data : console.log(difference([1, 2, 3], [100, 2, 1, 10])); ["1", "2", "3", "10", "100"] console.log(difference([1, 2, 3, 4, 5], [1, [2], [3, [[4]]],[5,6]])); ["1", "2", "3", "4", "5", "6"] console.log(difference([1, 2, 3], [100, 2, 1, 10])); ["1", "2", "3", "10", "100"] Click me to see the solution

43. Write a JavaScript function to create an array of arrays, ungrouping the elements in an array produced by zip. Go to the editor

Test Data : unzip([['a', 1, true], ['b', 2, false]]) unzip([['a', 1, true], ['b', 2]]) Expected Output: [["a","b"],[1,2],[true,false]] [["a","b"],[1,2],[true]] Click me to see the solution

44. Write a JavaScript function to create an object from an array, using the specified key and excluding it from each value. Go to the editor

Test Data : indexOn([ { id: 10, name: 'apple' }, { id: 20, name: 'orange' } ], x => x.id) Expected Output: {"undefined":{"id":20,"name":"orange"}} Click me to see the solution

45. Write a JavaScript program to find all unique values in an given array of numbers. Go to the editor

Test Data : [1, 2, 2, 3, 4, 4, 5] [1, 2, 3, 4, 5] [1, -2, -2, 3, 4, -5, -6, -5] Expected Output: [1,2,3,4,5] [1,2,3,4,5] [1,-2,3,4,-5,-6] Click me to see the solution

46. Write a JavaScript program to generate all permutations of an array's elements (contains duplicates). Go to the editor

Test Data : [1, 33, 5] [1, 3, 5, 7] [2, 4] Expected Output: [[1,33,5],[1,5,33],[33,1,5],[33,5,1],[5,1,33],[5,33,1]] [[1,3,5,7],[1,3,7,5],[1,5,3,7],[1,5,7,3],[1,7,3,5],[1,7,5,3],[3,1,5,7],[3,1,7,5],[3,5,1,7],[3,5,7,1],[3,7,1,5],[3,7,5,1],[5,1,3,7],[5,1,7,3],[5,3,1,7],[5,3,7,1],[5,7,1,3],[5,7,3,1],[7,1,3,5],[7,1,5,3],[7,3,1,5],[7,3,5,1],[7,5,1,3],[7,5,3,1]] [[2,4],[4,2]] Click me to see the solution

47. Write a JavaScript program to remove all falsy values from an given object or array. Go to the editor

Test Data : const obj = { a: null, b: false, c: true, d: 0, e: 1, f: '', g: 'a', h: [null, false, '', true, 1, 'a'], i: { j: 0, k: false, l: 'a' } Expected Output: {"c":true,"e":1,"g":"a","h":[true,1,"a"],"i":{"l":"a"}} Click me to see the solution

48. Write a JavaScript program that takes an array of integers and returns false if every number is not prime. Otherwise, return true. Go to the editor

Test Data : ([2,3,5,7]) -> true ([2,3,5,7,8]) -> false Expected Output: Original array of integers: 2,3,5,7 In the said array check every numbers are prime or not! true Original array of integers: 2,3,5,7,8 In the said array check every numbers are prime or not! false Click me to see the solution

49. Write a JavaScript program that takes an array of numbers and returns the third smallest number. Go to the editor

Test Data : (2,3,5,7,1) -> 3 (2,3,0,5,7,8,-2,-4) -> 0 Expected Output: Original array of numbers: 2,3,5,7,1 Third smallest number of the said array of numbers: 3 Original array of numbers: 2,3,0,5,7,8,-2,-4 Third smallest number of the said array of numbers: 0 Click me to see the solution

50. Write a JavaScript program that takes an array with mixed data type and calculate the sum of all numbers. Go to the editor

Test Data : ([2, "11", 3, "a2", false, 5, 7, 1]) -> 18 ([2, 3, 0, 5, 7, 8, true, false]) -> 25 Expected Output: Original array: 2,11,3,a2,false,5,7,1 Sum all numbers of the said array: 18 Original array: 2,3,0,5,7,8,true,false Sum all numbers of the said array: 25 Click me to see the solution

51. Write a JavaScript program to check if an array is a factor chain or not. Go to the editor

A factor chain is an array in which the previous element is a factor of the next consecutive element. The following is a factor chain: [2, 4, 8, 16, 32] // 2 is a factor of 4 // 4 is a factor of 8 // 8 is a factor of 16 // 16 is a factor of 32

Test Data : ([2, 4, 8, 16, 32]) -> true ([2, 4, 16, 32, 64]) -> true ([2, 4, 16, 32, 68]) -> false Expected Output: Original array: Check the said array is a factor chain or not? true Original array: Check the said array is a factor chain or not? true Original array: Check the said array is a factor chain or not? false Click me to see the solution

52. Write a JavaScript program to get all the indexes where NaN is found of a given array of numbers and NaN. Go to the editor

Test Data : ([2, NaN, 8, 16, 32]) -> [1] ([2, 4, NaN, 16, 32, NaN]) -> [2,5] ([2, 4, 16, 32]) ->[] Expected Output: Original array: 2,NaN,8,16,32 Find all indexes of NaN of the said array: 1 Original array: 2,4,NaN,16,32,NaN Find all indexes of NaN of the said array: 2,5 Original array: 2,4,16,32 Find all indexes of NaN of the said array: Click me to see the solution

53. Write a JavaScript program to count the number of arrays inside a given array. Go to the editor

Test Data : ([2,8,[6],3,3,5,3,4,[5,4]]) -> 2 ([2,8,[6,3,3],[4],5,[3,4,[5,4]]]) -> 3 Expected Output: Number of arrays inside the said array: 2 Number of arrays inside the said array: 3 Click me to see the solution

* To run the code mouse over on Result panel and click on 'RERUN' button. *

See the Pen javascript-common-editor by w3resource ( @w3resource ) on CodePen .

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Alternative of Object.assign(...array)

Assume we have array of objects.

Calling Object.assign(...array) makes an inheritance among those objects where object with index i override existing properties in object with index i-1

var array=[{interf:'IPerson',name:'Someone'},{clss:'Person',name:'Ahmed'},{student:true}]; console.log( Object.assign(...array) // Object.assign(array[0],array[1],array[2]) )

Now, using Babel with the proposed object spread syntax, we can do this statically :

How to do that dynamically?

There is overlap of context of "spread syntax". I mean how to use spread syntax for both:

I tried {...array} and it returns {0:<array[0]>,1:<array[1]>,2:<array[2]>} which is not the same output as Object.assign(...array) .

ecmascript-next

4 Answers 4

You are looking for

that creates a new object instead of mutating array[0] .

Seems to me the method you're looking for is .concat()

Returns a new array which is a merge of the target and the source.

I thing the method you are looking for, as mentioned above, is .concat() , which creates a copy of an array and extends it with another one.

Assign Objects with array object:

var a = { 'name': 'Ajay' } var b = { approvers: [{ id: '12' }] } var c = Object.assign(a, b); console.log(c);

The variable a and b are type of an object and not an array – supritshah1289 Jun 14, 2022 at 15:57

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JavaScript Arrays: Create, Access, Add & Remove Elements

We have learned that a variable can hold only one value. We cannot assign multiple values to a single variable. JavaScript array is a special type of variable, which can store multiple values using a special syntax.

The following declares an array with five numeric values.

In the above array, numArr is the name of an array variable. Multiple values are assigned to it by separating them using a comma inside square brackets as [10, 20, 30, 40, 50] . Thus, the numArr variable stores five numeric values. The numArr array is created using the literal syntax and it is the preferred way of creating arrays.

Another way of creating arrays is using the Array() constructor, as shown below.

Every value is associated with a numeric index starting with 0. The following figure illustrates how an array stores values.

assignment on javascript array

The following are some more examples of arrays that store different types of data.

It is not required to store the same type of values in an array. It can store values of different types as well.

Get Size of an Array

Use the length property to get the total number of elements in an array. It changes as and when you add or remove elements from the array.

Accessing Array Elements

Array elements (values) can be accessed using an index. Specify an index in square brackets with the array name to access the element at a particular index like arrayName[index] . Note that the index of an array starts from zero.

For the new browsers, you can use the arr.at(pos) method to get the element from the specified index. This is the same as arr[index] except that the at() returns an element from the last element if the specified index is negative.

You can iterate an array using Array.forEach() , for, for-of, and for-in loop, as shown below.

Update Array Elements

You can update the elements of an array at a particular index using arrayName[index] = new_value syntax.

Adding New Elements

You can add new elements using arrayName[index] = new_value syntax. Just make sure that the index is greater than the last index. If you specify an existing index then it will update the value.

In the above example, cities[9] = "Pune" adds "Pune" at 9th index and all other non-declared indexes as undefined.

The recommended way of adding elements at the end is using the push() method. It adds an element at the end of an array.

Use the unshift() method to add an element to the beginning of an array.

Remove Array Elements

The pop() method returns the last element and removes it from the array.

The shift() method returns the first element and removes it from the array.

You cannot remove middle elements from an array. You will have to create a new array from an existing array without the element you do not want, as shown below.

Learn about array methods and properties in the next chapter.

Related Articles

Destructuring Assignment in JavaScript

Destructuring Assignment is a JavaScript expression that allows to unpack values from arrays, or properties from objects, into distinct variables data can be extracted from arrays, objects, nested objects and assigning to variables . In Destructuring Assignment on the left-hand side defined that which value should be unpacked from the sourced variable. In general way implementation of the extraction of the array is as shown below: Example:

Array destructuring:

Object destructuring:

Array destructuring: Using the Destructuring Assignment in JavaScript array possible situations, all the examples are listed below:

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JavaScript Destructuring Assignment

Object and Array are the two frequently used data structures of JavaScript.

With the help of the objects, you can create an entity storing data items by key. With the help of the arrays, you can assemble data items into an ordered collection.

In case of passing those to a function, it might need an object and array not as a whole but some individual pieces.

The literal expressions of the object and the array allow creating ad hoc packages. Here is the syntax:

The destructuring assignment is a unique syntax that helps “to unpack” objects or arrays into a group of variables. Destructuring can also operate efficiently with complex functions, default values, and more.

The destructuring assignment uses the following syntax:

You can find similar features in other languages too. For example, in Python or Perl.

Now, let’s have a look at the example of the array destructure into variables:

As a result, it is possible to work with variables instead of array members.

will work even greater if you combine it with split or other methods for array-returning:

Note that destructuring is not the same as “destructive”.

We call it destructuring as it “destructurizes” through the method of copying items into variables.

Here is a shorter way to write:

Take into consideration that you can throw away unwanted elements by using an extra comma, like this:

It can work with any iterable on the right-side:

Moreover, you can use any assignables at the left side.

For example, the property of an object:

Another useful thing is that it is possible to use the Object.entries(obj) method with destructuring for looping over keys-and-values of an object.

Here is an example:

The rest ‘…’

In case it is necessary to get not only the first values but also to assemble all the followings, you have the option of adding another parameter for getting “the rest” by just using three dots “…” , like this:

In case there are fewer values in the array than variables in the assignment, no error will occur. The values that are absent will be considered undefined:

If you want a default value for replacing the one that is missing, use the = sign, as follows:

Destructuring an Object

You can use the destructuring assignment with objects, as well, by using the following basic syntax:

On the right side, there is an existing object that is necessary to split into variables. On the left side, there is a pattern for matching properties. The three dots sign {...} includes a group of variable names.

The properties options.title , options.width and options.height are assigned to matching variables. The arrangement doesn’t matter. This option will also work:

For assigning a property to a variable with different name, then you can act like this:

For possible missing properties, you have the option of setting default values using the sign of “=” , as follows:

The default values might be any expressions or function calls.

In case there is a complex object with a range of properties, you may choose to extract what you need, as follows:

The Rest Pattern “…”

Another scenario can also happen: the quantity of the object properties is more than the variables you have. In such cases, you can use the rest pattern. But, note that it works only on modern browsers.

Here is the example:

Nested Destructuring

Imagine that an array or an object includes other nested arrays or objects. More complex, left-side patterns might be used for extracting deeper portions.

In the example below, options contain another object in the property views and array in the property items :

It’s important to know that all the properties of options object except extra (it’s absent at the left side), are assigned to matching variables.

So, the model , year , item1 , item2 , and title are of the same value. But, no variables exist for views and items .

The Parameters of Smart Function

Sometimes a function has many parameters, and most of them are optional. But, let’s see that a function creates a menu. It will have a height, width, items list, a title, and more.

We don’t recommend you to write the function, like this:

The main problem is remembering the order of the arguments. Another problem is to find a way of calling a function when the majority of the parameters are good by default.

The most optional action is passing parameters as an object. The function will destructurize them into a variable at once, like this:

There is another, more complex way of destructuring, including nested objects and colon mappings.

The full syntax will look like this:

As you can see, it’s the same as for a destructuring assignment.

Then, for the parameters’ object, there will be a variable varName for incomingProperty .

Destructuring like this considers that showBook() has no argument. In case you want all the values by default, then specify an empty object, like this:

It is possible to fix it by setting {} the default value the object of parameters.

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COMMENTS

Destructuring assignment
The destructuring assignment syntax is a JavaScript expression that makes it possible to unpack values from arrays, or properties from
Array
The Array object, as with arrays in other programming languages, enables storing a collection of multiple items under a single variable name
JavaScript Arrays
Using an array literal is the easiest way to create a JavaScript Array. Syntax: const array_name = [item1, item2, ...];.
Hacks for Creating JavaScript Arrays
In JavaScript, arrays and objects are reference types. This means that when a variable is assigned an array or object, what gets assigned to the
Destructuring assignment
Arrays allow us to gather data items into an ordered list. Although, when we pass those to a function, it may need not be an object/array as a
JavaScript Arrays (with Examples)
However, it is not recommended to store values by passing arbitrary names
JavaScript array
JavaScript array [53 exercises with solution] · 1. Write a JavaScript function to check whether an `input` is an array or not. · 2. Write a
Alternative of Object.assign(...array)
You are looking for var obj = Object.assign({}, ...array). that creates a new object instead of mutating array[0] .
JavaScript Arrays: Create, Access, Add & Remove Elements
We have learned that a variable can hold only one value. We cannot assign multiple values to a single variable. JavaScript array is a special type of variable
Destructuring Assignment in JavaScript
Destructuring Assignment is a JavaScript expression that allows to unpack values from arrays, or properties from objects, into distinct
Destructuring Assignment In JavaScript
Object and Array are the two frequently used data structures of JavaScript. With the help of the objects, you can create an entity storing data items by key