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JavaScript Array Methods


The strength of JavaScript arrays lies in the array methods.


Converting Arrays to Strings

The JavaScript method toString() converts an array to a string of (comma separated) array values.

Example

var fruits = ["Banana", "Orange", "Apple", "Mango"];
document.getElementById("demo").innerHTML = fruits.toString();

Result

Banana,Orange,Apple,Mango
Try it Yourself »

The join() method also joins all array elements into a string.

It behaves just like toString(), but in addition you can specify the separator:

Example

var fruits = ["Banana", "Orange","Apple", "Mango"];
document.getElementById("demo").innerHTML = fruits.join(" * ");

Result

Banana * Orange * Apple * Mango
Try it Yourself »

Popping and Pushing

When you work with arrays, it is easy to remove elements and add new elements.

This is what popping and pushing is:

Popping items out of an array, or pushing items into an array.


Popping

The pop() method removes the last element from an array:

Example

var fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits.pop();              // Removes the last element ("Mango") from fruits
Try it Yourself »

The pop() method returns the value that was "popped out":

Example

var fruits = ["Banana", "Orange", "Apple", "Mango"];
var x = fruits.pop();      // the value of x is "Mango"
Try it Yourself »

Pushing

The push() method adds a new element to an array (at the end):

Example

var fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits.push("Kiwi");       //  Adds a new element ("Kiwi") to fruits
Try it Yourself »

The push() method returns the new array length:

Example

var fruits = ["Banana", "Orange", "Apple", "Mango"];
var x = fruits.push("Kiwi");   //  the value of x is 5
Try it Yourself »

Shifting Elements

Shifting is equivalent to popping, working on the first element instead of the last.

The shift() method removes the first array element and "shifts" all other elements to a lower index.

Example

var fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits.shift();            // Removes the first element "Banana" from fruits
Try it Yourself »

The unshift() method adds a new element to an array (at the beginning), and "unshifts" older elements:

Example

var fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits.unshift("Lemon");    // Adds a new element "Lemon" to fruits
Try it Yourself »

The shift() method returns the string that was "shifted out".

The unshift() method returns the new array length.


Changing Elements

Array elements are accessed using their index number:

Note Array indexes start with 0. [0] is the first array element, [1] is the second, [2] is the third ....

Example

var fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits[0] = "Kiwi";        // Changes the first element of fruits to "Kiwi"
Try it Yourself »

The length property provides an easy way to append a new element to an array:

Example

var fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits[fruits.length] = "Kiwi";          // Appends "Kiwi" to fruit
Try it Yourself »

Deleting Elements

Since JavaScript arrays are objects, elements can be deleted by using the JavaScript operator delete:

Example

var fruits = ["Banana", "Orange", "Apple", "Mango"];
delete fruits[0];           // Changes the first element in fruits to undefined
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Note Using delete on array elements leaves undefined holes in the array. Use pop() or shift() instead.


Splicing an Array

The splice() method can be used to add new items to an array:

Example

var fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits.splice(2, 0, "Lemon", "Kiwi");
Try it Yourself »

The first parameter (2) defines the position where new elements should be added (spliced in).

The second parameter (0) defines how many elements should be removed.

The rest of the parameters ("Lemon" , "Kiwi") define the new elements to be added.


Using splice() to Remove Elements

With clever parameter setting, you can use splice() to remove elements without leaving "holes" in the array:

Example

var fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits.splice(0, 1);        // Removes the first element of fruits
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The first parameter (0) defines the position where new elements should be added (spliced in).

The second parameter (1) defines how many elements should be removed.

The rest of the parameters are omitted. No new elements will be added.


Sorting an Array

The sort() method sorts an array alphabetically:

Example

var fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits.sort();            // Sorts the elements of fruits
Try it Yourself »

Reversing an Array

The reverse() method reverses the elements in an array.

You can use it to sort an array in descending order:

Example

var fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits.sort();            // Sorts the elements of fruits
fruits.reverse();         // Reverses the order of the elements
Try it Yourself »

Numeric Sort

By default, the sort() function sorts values as strings.

This works well for strings ("Apple" comes before "Banana").

However, if numbers are sorted as strings, "25" is bigger than "100", because "2" is bigger than "1".

Because of this, the sort() method will produce incorrect result when sorting numbers.

You can fix this by providing a compare function:

Example

var points = [40, 100, 1, 5, 25, 10];
points.sort(function(a, b){return a-b});
Try it Yourself »

or

Example

var points = [40, 100, 1, 5, 25, 10];
points.sort(function(a, b){return a>b});
Try it Yourself »

Use the same trick to sort an array descending:

Example

var points = [40, 100, 1, 5, 25, 10];
points.sort(function(a, b){return b-a});
Try it Yourself »

or

Example

var points = [40, 100, 1, 5, 25, 10];
points.sort(function(a, b){return b>a});
Try it Yourself »

The Compare Function

The purpose of the compare function is to define an alternative sort order.

The compare function should return a negative, zero, or positive value, depending on the arguments:

function(a, b){return a-b}

When the sort() function compares two values, it sends the values to the compare function, and sorts the values according to the returned (negative, zero, positive) value.

Example:

When comparing 40 and 100, the sort() method calls the compare function(40,100).

The function calculates 40-100, and returns -60 (a negative value).

The sort function will sort 40 as a value lower than 100.


Find the Highest (or Lowest) Value

How to find the highest value in an array?

Example

var points = [40, 100, 1, 5, 25, 10];
points.sort(function(a, b){return b-a});
// now points[0] contains the highest value
Try it Yourself »

And the lowest:

Example

var points = [40, 100, 1, 5, 25, 10];
points.sort(function(a, b){return a-b});
// now points[0] contains the lowest value
Try it Yourself »

Joining Arrays

The concat() method creates a new array by concatenating two arrays:

Example

var myGirls = ["Cecilie", "Lone"];
var myBoys = ["Emil", "Tobias","Linus"];
var myChildren = myGirls.concat(myBoys);     // Concatenates (joins) myGirls and myBoys
Try it Yourself »

The concat() method can take any number of array arguments:

Example

var arr1 = ["Cecilie", "Lone"];
var arr2 = ["Emil", "Tobias","Linus"];
var arr3 = ["Robin", "Morgan"];
var myChildren = arr1.concat(arr2, arr3);     // Concatenates arr1 with arr2 and arr3
Try it Yourself »

Slicing an Array

The slice() method slices out a piece of an array into a new array.

This example slices out a part of an array starting from array element 1 ("Orange"):

Example

var fruits = ["Banana", "Orange", "Lemon", "Apple", "Mango"];
var citrus = fruits.slice(1);
Try it Yourself »
Note Array indexes start with 0. [0] is the first array element, [1] is the second, [2] is the third ....

This example slices out a part of an array starting from array element 3 ("Apple"):

Example

var fruits = ["Banana", "Orange", "Lemon", "Apple", "Mango"];
var citrus = fruits.slice(3);
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The slice() method can take two arguments like slice(1,3).

The method then selects elements from the start argument, and up to (but not including) the end argument.

Example

var fruits = ["Banana", "Orange", "Lemon", "Apple", "Mango"];
var citrus = fruits.slice(1, 3);
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If the end argument is omitted, like in the first examples, the slice() method slices out the rest of the array.

Example

var fruits = ["Banana", "Orange", "Lemon", "Apple", "Mango"];
var citrus = fruits.slice(2);
Try it Yourself »

The valueOf() Method

The valueOf() method is the default behavior for an array. It converts an array to a primitive value.

JavaScript will automatically convert an array to a string when a primitive value is expected.

Because of this, all these examples will produce the same result:

Example

var fruits = ["Banana", "Orange", "Apple", "Mango"];
document.getElementById("demo").innerHTML = fruits;
Try it Yourself »

Example

var fruits = ["Banana", "Orange", "Apple", "Mango"];
document.getElementById("demo").innerHTML = fruits.valueOf();
Try it Yourself »

Example

var fruits = ["Banana", "Orange", "Apple", "Mango"];
document.getElementById("demo").innerHTML = fruits.toString();
Try it Yourself »
Note All JavaScript objects have the valueOf() and toString() methods.

Complete Array Reference

For a complete reference, go to our Complete JavaScript Array Reference.

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


Test Yourself with Exercises!

Exercise 1 »  Exercise 2 »  Exercise 3 »  Exercise 4 »  Exercise 5 »