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]
Oldest comments (34)
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];?
I think it's more likely to compare it to the array constructor. According to MDN
I didn't know this method either!
Thanks, I didn't know about that !
He asked about [1, 2, 3, 4, 5, 6] and not Array(7), is it the same?
it is essentially the same, I just pointed out what is a better comparison case with quote from the mdn docs
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)
Thanks for the article Frugence! 👍
I would like to use
[...] SpreadOperatora shorthand alternate toArray.from()I wonder is there any major difference between these 2 ways?
Take a look here friend, Array.from() vs spread syntax
Thanks for the reference friend. 👍
You are welcome friend
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.Hi Frugence. Is it possible to also outline which ones are supported by ES5 browsers etc.
MDNs documentation covers every array.prototype method, and which browsers that supports which methods:
developer.mozilla.org/en-US/docs/W...
Hi buddy, try this caniuse.com
This is a great article with succinct and concrete examples. Thanks!
This is great thank you!
Thanks for the article man.great stuff
Thanks for the article. Opened my eyes to so many ways to manipulate arrays.
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.You can thank MooTools for that: github.com/tc39/Array.prototype.in...
... 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.
You ever heard that a black background color makes reading more difficult?
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.
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:
..then both variables will contain the same thing:
With this in mind, your example could be simplified to the following:
Great Post!
Very nice useful methods man! but it's not so clear the forEach() example. Anyway, thank you
This is really very helpful. Thanks for this article.
You are welcome friend
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
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.My main use case for using
.forEachbefore discovering.reducewas because I wanted to transform one object into a new object with a different shape. I'd create an empty object and then.forEachthe original object's Object.entities/keys to add properties to the empty object, whereas this is more concise by simply using a.reduce