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]