JavaScript forEach 10 JavaScript array methods you should know

This post is originally published to my blog.

In this post i will share 10 JavaScript array methods you should know.

If you know nothing about array, you can click here for array introduction.

Here are 10 javascript array methods you should at least know

1. forEach()

This method can help you to loop over array's items.

  const arr = [1, 2, 3, 4, 5, 6];

  arr.forEach(item => {
    console.log(item); // output: 1 2 3 4 5 6
  });

2. includes()

This method check if array includes the item passed in the method.

  const arr = [1, 2, 3, 4, 5, 6];

  arr.includes(2); // output: true
  arr.includes(7); // output: false

3. filter()

This method create new array with only elements passed condition inside the provided function.

  const arr = [1, 2, 3, 4, 5, 6];

  // item(s) greater than 3
  const filtered = arr.filter(num => num > 3);
  console.log(filtered); // output: [4, 5, 6]

  console.log(arr); // output: [1, 2, 3, 4, 5, 6]

4. map()

This method create new array by calling the provided function in every element.

  const arr = [1, 2, 3, 4, 5, 6];

  // add one to every element
  const oneAdded = arr.map(num => num + 1);
  console.log(oneAdded); // output [2, 3, 4, 5, 6, 7]

  console.log(arr); // output: [1, 2, 3, 4, 5, 6]

5. reduce()

The reduce() method applies a function against an accumulator and each element in the array (from left to right) to reduce it to a single value - MDN

  const arr = [1, 2, 3, 4, 5, 6];

  const sum = arr.reduce((total, value) => total + value, 0);
  console.log(sum); // 21

6. some()

This method check if at least one of array's item passed the condition. If passed, it return 'true' otherwise 'false'.

  const arr = [1, 2, 3, 4, 5, 6];

  // at least one element is greater than 4?
  const largeNum = arr.some(num => num > 4);
  console.log(largeNum); // output: true

  // at least one element is less than or equal to 0?
  const smallNum = arr.some(num => num <= 0);
  console.log(smallNum); // output: false

7. every()

This method check if all array's item passed the condition. If passed, it return 'true' otherwise 'false'.

  const arr = [1, 2, 3, 4, 5, 6];

  // all elements are greater than 4
  const greaterFour = arr.every(num => num > 4);
  console.log(greaterFour); // output: false

  // all elements are less than 10
  const lessTen = arr.every(num => num < 10);
  console.log(lessTen); // output: true

8. sort()

This method used to arrange/sort array's item either ascending or descending order.

  const arr = [1, 2, 3, 4, 5, 6];
  const alpha = ['e', 'a', 'c', 'u', 'y'];

  // sort in descending order
  descOrder = arr.sort((a, b) => a > b ? -1 : 1);
  console.log(descOrder); // output: [6, 5, 4, 3, 2, 1]

  // sort in ascending order
  ascOrder = alpha.sort((a, b) => a > b ? 1 : -1);
  console.log(ascOrder); // output: ['a', 'c', 'e', 'u', 'y']

9. Array.from()

This change all thing that are array-like or iterable into true array especially when working with DOM, so that you can use other array methods like reduce, map, filter and so on.

  const name = 'frugence';
  const nameArray = Array.from(name);

  console.log(name); // output: frugence
  console.log(nameArray); // output: ['f', 'r', 'u', 'g', 'e', 'n', 'c', 'e']

working with DOM

  // I assume that you have created unorder list of items in our html file.

  const lis = document.querySelectorAll('li');
  const lisArray = Array.from(document.querySelectorAll('li'));

  // is true array?
  console.log(Array.isArray(lis)); // output: false
  console.log(Array.isArray(lisArray));  // output: true

10. Array.of()

This create array from every arguments passed into it.

  const nums = Array.of(1, 2, 3, 4, 5, 6);
  console.log(nums); // output: [1, 2, 3, 4, 5, 6]

Comments

[Thiru]

Thanks for the article Frugence! 👍

I would like to use [...] SpreadOperator a shorthand alternate to Array.from()

const lisArray = [... document.querySelectorAll('li')];

I wonder is there any major difference between these 2 ways?

[Frugence Fidel]

Take a look here friend, Array.from() vs spread syntax

[Daniel Tonon]

Based on that, the answer is essentially "no, they are practically the same" for most use cases.

For some edge cases they do have differences. In those specific edge cases Array.from() is the better one to use.

[Thiru]

Thanks for the reference friend. 👍

[Frugence Fidel]

You are welcome friend

[Nans Dumortier]

Hey! Thanks for your article 😃
I knew most of them, except the last one. By the way, I was wondering : in which case :
const nums = Array.of(1, 2, 3, 4, 5, 6);
is better than :
const nums = [1, 2, 3, 4, 5, 6];
?

[Wouter Lievens]

It's the same, but one is a function whereas the other is a syntactical form. You could have a situation where you pass it as a parameter or in a variable, i.e.

f = Array.of
...
a = f(1,2,3)

[Angel Daniel Munoz Gonzalez]

I think it's more likely to compare it to the array constructor. According to MDN

The difference between Array.of() and the Array constructor is in the handling of integer arguments: Array.of(7) creates an array with a single element, 7, whereas Array(7) creates an empty array with a length property of 7 (Note: this implies an array of 7 empty slots, not slots with actual undefined values).

I didn't know this method either!

[Nans Dumortier]

Thanks, I didn't know about that !

[Warix3]

He asked about [1, 2, 3, 4, 5, 6] and not Array(7), is it the same?

[Angel Daniel Munoz Gonzalez]

it is essentially the same, I just pointed out what is a better comparison case with quote from the mdn docs

[Martin Häusler]

Does anybody else think that Array#includes(...) is a failure in naming? Every other core library I can think of right now (Java, C#, Kotlin...) calls it #contains(...). Except for JavaScript. I stumble upon that every time I need it, I have to look it up.

[Patrick Connors]

You can thank MooTools for that: github.com/tc39/Array.prototype.in...

This proposal was formerly for Array.prototype.contains, but that name [is not web-compatible](https://esdiscuss.org/topic/having-a-non-enumerable-array-prototype-contains-may-not-be-web-compatible). Per the November 2014 TC39 meeting, the name of both String.prototype.contains and Array.prototype.contains was changed to includes to dodge that bullet.

[Martin Häusler]

... and every programmer ever since (who did not start out with JS as their first language) bites that very bullet that they were trying to dodge. Just because of one library? Hahaha, made my day, this is so very web-like.

[Tommy Long]

My personal tip is learn .reduce as soon as possible. It intimidated me for a long time and I used .forEach a lot. Once you get reduce you'll suddenly realise how powerful and straight-forward it is and basically never use .forEach again

[Elliot Derhay]

Isn't reduce mainly for working with current values and a total value? How would that take the place of something like .forEach() entirely?

Granted, I do think I have a use case for it, but I don't yet see the need for replacing something like .forEach() or .map() entirely.

[Tommy Long]

My main use case for using .forEach before discovering .reduce was because I wanted to transform one object into a new object with a different shape. I'd create an empty object and then .forEach the original object's Object.entities/keys to add properties to the empty object, whereas this is more concise by simply using a .reduce

[Andre Greeff]

There's one critical point of .sort() that I feel you should mention in the article: the .sort() method sorts an array in place, it does not return a sorted copy of the array...

Basically, if you do the following:

const myThings = [5,2,4,3,6,1];
const sortedThings = myThings.sort();

..then both variables will contain the same thing:

myThings; // [1,2,3,4,5,6]
sortedThings; // [1,2,3,4,5,6]
myThings === sortedThings; // true

---

With this in mind, your example could be simplified to the following:

const arr = [1, 2, 3, 4, 5, 6];
const alpha = ['e', 'a', 'c', 'u', 'y'];

// sort in descending order
arr.sort((a, b) => a > b ? -1 : 1);
console.log(arr); // output: [6, 5, 4, 3, 2, 1]

// sort in ascending order
alpha.sort((a, b) => a > b ? 1 : -1);
console.log(alpha); // output: ['a', 'c', 'e', 'u', 'y']

[Michael Roberts]

Hi Frugence. Is it possible to also outline which ones are supported by ES5 browsers etc.

[Philip Karlsson]

MDNs documentation covers every array.prototype method, and which browsers that supports which methods:

developer.mozilla.org/en-US/docs/W...

[Frugence Fidel]

Hi buddy, try this caniuse.com

[Daan Wilmer]

Your explanation for sort is incomplete. First of all, you don't have to provide a comparison function - although the array is then sorted by text value ascending. ['bob', 'alice', 'barbara'] gets sorted as expected, [3, 4, 21 100] does not (it becomes [100, 21, 3, 4]).

More importantly, though: the comparison function is expected to return 0 (zero) when the two elements are equal. Although the used sorting algorithm can probably deal without this, it's still better to return 0 to conform to the spec. It might even speed up the code in certain specific cases.

[Elliot Derhay]

Thanks for mentioning performance, though I avoid for loops for stuff like this now after too many times having the loop somehow end up using only the last value in the array for all iterations.

[Matthew Brown]

This is great thank you!

[Hridayesh Sharma]

This is really very helpful. Thanks for this article.

[Frugence Fidel]

You are welcome friend