JavaScript Array Methods
Basic Array Methods
JavaScript Array length
The length property returns the length (size) of an array:
Example
const fruits = ["Banana", "Orange", "Apple", "Mango"];
let size = fruits.length;
Try it Yourself »
JavaScript Array toString()
The JavaScript method toString() converts an array to a
string of (comma separated) array values.
Example
const fruits = ["Banana", "Orange", "Apple", "Mango"];
document.getElementById("demo").innerHTML = fruits.toString();
Result:
JavaScript Array at()
ES2022 intoduced the array method at():
Examples
Get the third element of fruits using at():
const fruits = ["Banana", "Orange", "Apple", "Mango"];
let fruit = fruits.at(2);
Try it Yourself »
Get the third element of fruits using []:
const fruits = ["Banana", "Orange", "Apple", "Mango"];
let fruit = fruits[2];
Try it Yourself »
The at() method returns an indexed element from an array.
The at() method returns the same as [].
The at() method is supported in all modern browsers since March 2022:
| Chrome 92 | Edge 92 | Firefox 90 | Safari 15.4 | Opera 78 |
| Apr 2021 | Jul 2021 | Jul 2021 | Mar 2022 | Aug 2021 |
Note
Many languages allows negative bracket indexing like [-1] to access elements from the end of an
object / array / string.
This is not possible in JavaScript, because [] is used for accessing both arrays and objects. obj[-1] refers to the value of key -1, not to the last property of the object.
The at() method was introduced in ES2022 to solve this problem.
JavaScript Array join()
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
const fruits = ["Banana", "Orange", "Apple", "Mango"];
document.getElementById("demo").innerHTML = fruits.join(" * ");
Result:
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.
JavaScript Array pop()
The pop() method removes the last element from an array:
The pop() method returns the value that was "popped out":
Example
const fruits = ["Banana", "Orange", "Apple", "Mango"];
let fruit = fruits.pop();
Try it Yourself »
JavaScript Array push()
The push() method adds a new element to an array (at the end):
Example
const fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits.push("Kiwi");
Try it Yourself »
The push() method returns the new array length:
Example
const fruits = ["Banana", "Orange", "Apple", "Mango"];
let length = fruits.push("Kiwi");
Try it Yourself »Shifting Elements
Shifting is equivalent to popping, but working on the first element instead of the last.
JavaScript Array shift()
The shift() method removes the first array element and "shifts" all
other elements to a lower index.
The shift() method returns the value that was "shifted out":
Example
const fruits = ["Banana", "Orange", "Apple", "Mango"];
let fruit = fruits.shift();
Try it Yourself »
JavaScript Array unshift()
The unshift() method adds a new element to an array (at the beginning), and "unshifts"
older elements:
Example
const fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits.unshift("Lemon");
Try it Yourself »
The unshift() method returns the new array length:
Example
const fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits.unshift("Lemon");
Try it Yourself »
Changing Elements
Array elements are accessed using their index number:
Array indexes start with 0:
[0] is the first array element
[1] is the second
[2] is the third ...
Example
const fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits[0] = "Kiwi";
Try it Yourself »
JavaScript Array length
The length property provides an easy way to append a new element to an array:
Example
const fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits[fruits.length] = "Kiwi";
Try it Yourself »
JavaScript Array delete()
Warning !
Using delete() leaves undefined holes in the
array.
Use pop() or shift() instead.
Merging Arrays (Concatenating)
In programming languages, concatenation means joining strings end-to-end.
Concatenation "snow" and "ball" gives "snowball".
Concatenating arrays means joining arrays end-to-end.
JavaScript Array concat()
The concat() method creates a new array by merging (concatenating)
existing arrays:
Example (Merging Two Arrays)
const myGirls = ["Cecilie", "Lone"];
const myBoys = ["Emil", "Tobias", "Linus"];
const myChildren = myGirls.concat(myBoys);
Try it Yourself »
Note
The concat() method does not change the existing arrays. It always returns a new array.
The concat() method can take any number of array arguments.
Example (Merging Three Arrays)
const arr1 = ["Cecilie", "Lone"];
const arr2 = ["Emil", "Tobias", "Linus"];
const arr3 = ["Robin", "Morgan"];
const myChildren = arr1.concat(arr2, arr3);
Try it Yourself »
The concat() method can also take strings as arguments:
Example (Merging an Array with Values)
const arr1 = ["Emil", "Tobias", "Linus"];
const myChildren = arr1.concat("Peter");
Try it Yourself »
Array copyWithin()
The copyWithin() method copies array elements to another position in an array:
Examples
Copy to index 2, all elements from index 0:
const fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits.copyWithin(2, 0);
Try it Yourself »
Copy to index 2, the elements from index 0 to 2:
const fruits = ["Banana", "Orange", "Apple", "Mango", "Kiwi"];
fruits.copyWithin(2, 0, 2);
Try it Yourself »
Note
The copyWithin() method overwrites the existing values.
The copyWithin() method does not add items to the array.
The copyWithin() method does not change the length of the array.
Flattening an Array
Flattening an array is the process of reducing the dimensionality of an array.
Flattening is useful when you want to convert a multi-dimensional array into a one-dimensional array.
JavaScript Array flat()
ES2019 Introduced the Array flat() method.
The flat() method creates a new array with sub-array elements concatenated to a specified depth.
Browser Support
JavaScript Array flat() is supported in all modern browsers since January 2020:
| Chrome 69 | Edge 79 | Firefox 62 | Safari 12 | Opera 56 |
| Sep 2018 | Jan 2020 | Sep 2018 | Sep 2018 | Sep 2018 |
JavaScript Array flatMap()
ES2019 added the Array flatMap() method to JavaScript.
The flatMap() method first maps all elements of an array
and then creates a new array by flattening the array.
Example
const myArr = [1, 2, 3, 4, 5, 6];
const newArr = myArr.flatMap(x => [x, x * 10]);
Try it Yourself »
Browser Support
JavaScript Array flatMap() is supported in all modern browsers since January 2020:
| Chrome 69 | Edge 79 | Firefox 62 | Safari 12 | Opera 56 |
| Sep 2018 | Jan 2020 | Sep 2018 | Sep 2018 | Sep 2018 |
Splicing and Slicing Arrays
The splice() method adds new items to an array.
The slice() method slices out a piece of an array.
JavaScript Array splice()
The splice() method can be used to add new items to an array:
Example
const 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.
The splice() method returns an array with the deleted items:
Example
const fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits.splice(2, 2, "Lemon", "Kiwi");
Try it Yourself »
Using splice() to Remove Elements
With clever parameter setting, you can use splice() to remove elements without leaving
"holes" in the array:
Example
const fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits.splice(0, 1);
Try it Yourself »
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.
JavaScript Array toSpliced()
ES2023 added the Array toSpliced() method as a safe way to splice an array without altering the original array.
The difference between the new toSpliced() method and the old splice() method is that the new method creates a new array, keeping the original array unchanged, while the old method altered the original array.
Example
const months = ["Jan", "Feb", "Mar", "Apr"];
const spliced = months.toSpliced(0, 1);
Try it Yourself »
JavaScript Array slice()
The slice() method slices out a piece of an array into a new
array:
Example
Slice out a part of an array starting from array element 1 ("Orange"):
const fruits = ["Banana", "Orange", "Lemon", "Apple", "Mango"];
const citrus = fruits.slice(1);
Try it Yourself »
Note
The slice() method creates a new array.
The slice() method does not remove any elements from the source array.
Example
Slice out a part of an array starting from array element 3 ("Apple"):
const fruits = ["Banana", "Orange", "Lemon", "Apple", "Mango"];
const citrus = fruits.slice(3);
Try it Yourself »
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
const fruits = ["Banana", "Orange", "Lemon", "Apple", "Mango"];
const citrus = fruits.slice(1, 3);
Try it Yourself »
If the end argument is omitted, like in the first examples, the slice()
method slices out the rest of the array.
Example
const fruits = ["Banana", "Orange", "Lemon", "Apple", "Mango"];
const citrus = fruits.slice(2);
Try it Yourself »
Automatic toString()
JavaScript automatically converts an array to a comma separated string when a primitive value is expected.
This is always the case when you try to output an array.
These two examples will produce the same result:
Example
const fruits = ["Banana", "Orange", "Apple", "Mango"];
document.getElementById("demo").innerHTML = fruits.toString();
Try it Yourself »
Example
const fruits = ["Banana", "Orange", "Apple", "Mango"];
document.getElementById("demo").innerHTML = fruits;
Try it Yourself »
Note
All JavaScript objects have a toString() method.
Searching Arrays
Searching arrays are covered in the next chapter of this tutorial.
Sorting Arrays
Sorting arrays covers the methods used to sort arraysg.
Iterating Arrays
Iterating arrays covers methods that operate on all array elements.
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.
