Let's understand javascript array functions and how to use them.

Array.map()

Returns a new array with the results of calling a provided function on every element in this array.

const list = [😫, 😫, 😫, 😫];
list.map((⚪️) => 😀); // [😀, 😀, 😀, 😀]

// Code
const list = [1, 2, 3, 4];
list.map((el) => el * 2); // [2, 4, 6, 8]

Array.filter()

Returns a new array with all elements that pass the test implemented by the provided function.

const list = [😀, 😫, 😀, 😫];
list.filter((⚪️) => ⚪️ === 😀); // [😀, 😀]

// Code
const list = [1, 2, 3, 4];
list.filter((el) => el % 2 === 0); // [2, 4]

Array.reduce()

Reduce the array to a single value. The value returned by the function is stored in an accumulator (result/total).

const list = [😀, 😫, 😀, 😫, 🤪];
list.reduce((⬜️, ⚪️) => ⬜️ + ⚪️); // 😀 + 😫 + 😀 + 😫 + 🤪

// OR
const list = [1, 2, 3, 4, 5];
list.reduce((total, item) => total + item, 0); // 15

Array.reduceRight()

Executes a reducer function (that you provide) on each element of the array resulting in a single output value(from right to left).

const list = [😀, 😫, 😀, 😫, 🤪];
list.reduceRight((⬜️, ⚪️) => ⬜️ + ⚪️); // 🤪 + 😫 + 😀 + 😫 + 😀

// Code
const list = [1, 2, 3, 4, 5];
list.reduceRight((total, item) => total + item, 0); // 15

Array.fill()

Fill the elements in an array with a static value.

const list = [😀, 😫, 😀, 😫, 🤪];
list.fill(😀); // [😀, 😀, 😀, 😀, 😀]

// Code
const list = [1, 2, 3, 4, 5];
list.fill(0); // [0, 0, 0, 0, 0]

Array.find()

Returns the value of the first element in the array that satisfies the provided testing function. Otherwise undefined is returned.

const list = [😀, 😫, 😀, 😫, 🤪];
list.find((⚪️) => ⚪️ === 😀); // 😀
list.find((⚪️) => ⚪️ === 😝); // undefined

// Code
const list = [1, 2, 3, 4, 5];
list.find((el) => el === 3); // 3
list.find((el) => el === 6); // undefined

Array.indexOf()

Returns the first index at which a given element can be found in the array, or -1 if it is not present.

const list = [😀, 😫, 😀, 😫, 🤪];
list.indexOf(😀); // 0
list.indexOf(😡); // -1

// Code
const list = [1, 2, 3, 4, 5];
list.indexOf(3); // 2
list.indexOf(6); // -1

Array.lastIndexOf()

Returns the last index at which a given element can be found in the array, or -1 if it is not present. The array is searched backwards, starting at fromIndex.

const list = [😀, 😫, 😀, 😫, 🤪];
list.lastIndexOf(😀); // 3
list.lastIndexOf(😀, 1); // 0

// Code
const list = [1, 2, 3, 4, 5];
list.lastIndexOf(3); // 2
list.lastIndexOf(3, 1); // -1

Array.findIndex()

Returns the index of the first element in the array that satisfies the provided testing function. Otherwise -1 is returned.

const list = [😀, 😫, 😀, 😫, 🤪];
list.findIndex((⚪️) => ⚪️ === 😀); // 0

// You might be thinking how it's different from `indexOf` 🤔
const array = [5, 12, 8, 130, 44];
array.findIndex((element) => element > 13); // 3

// OR
const array = [{
  id: 😀
}, {
  id: 😫
}, {
  id: 🤪
}];

array.findIndex((element) => element.id === 🤪); // 2

Array.includes()

Returns true if the given element is present in the array.

const list = [😀, 😫, 😀, 😫, 🤪];
list.includes(😀); // true

// Code
const list = [1, 2, 3, 4, 5];
list.includes(3); // true
list.includes(6); // false

Array.pop()

Removes the last element from an array and returns that element.

const list = [😀, 😫, 😀, 😫, 🤪];
list.pop(); // 🤪
list; // [😀, 😫, 😀, 😫]

// Code
const list = [1, 2, 3, 4, 5];
list.pop(); // 5
list; // [1, 2, 3, 4]

Array.push()

Appends new elements to the end of an array, and returns the new length.

const list = [😀, 😫, 😀, 😫, 🤪];
list.push(😡); // 5
list; // [😀, 😫, 😀, 😫, 🤪, 😡]

// Code
const list = [1, 2, 3, 4, 5];
list.push(6); // 6
list; // [1, 2, 3, 4, 5, 6]

Array.shift()

Removes the first element from an array and returns that element.

const list = [😀, 😫, 😀, 😫, 🤪];
list.shift(); // 😀
list; // [😫, 😀, 😫, 🤪]

// Code
const list = [1, 2, 3, 4, 5];
list.shift(); // 1
list; // [2, 3, 4, 5]

Array.unshift()

Adds new elements to the beginning of an array, and returns the new length.

const list = [😀, 😫, 😀, 😫, 🤪];
list.unshift(😡); // 6
list; // [😡, 😀, 😫, 😀, 😫, 🤪]

// Code
const list = [1, 2, 3, 4, 5];
list.unshift(0); // 6
list; // [0, 1, 2, 3, 4, 5]

Array.splice()

Changes the contents of an array by removing or replacing existing elements and/or adding new elements in place.

const list = [😀, 😫, 😀, 😫, 🤪];
list.splice(1, 2); // [😀, 😫]
list; // [😀, 😫, 🤪]

// Code
const list = [1, 2, 3, 4, 5];
list.splice(1, 2); // [2, 3]
list; // [1, 4, 5]

Array.slice()

Returns a shallow copy of a portion of an array into a new array object selected from begin to end (end not included). The original array will not be modified.

const list = [😀, 😫, 😀, 😫, 🤪];
list.slice(1, 3); // [😫, 😀]
list; // [😀, 😫, 😀, 😫, 🤪]

// Code
const list = [1, 2, 3, 4, 5];
list.slice(1, 3); // [2, 3]
list; // [1, 2, 3, 4, 5]

Array.join()

Joins all elements of an array into a string.

const list = [😀, 😫, 😀, 😫, 🤪];
list.join('〰️'); // "😀〰️😫〰️😀〰️😫〰️🤪"

// Code
const list = [1, 2, 3, 4, 5];
list.join(', '); // "1, 2, 3, 4, 5"

Array.reverse()

Reverses the order of the elements in an array.

const list = [😀, 😫, 😀, 😫, 🤪];
list.reverse(); // [🤪, 😫, 😀, 😫, 😀]
list; // [🤪, 😫, 😀, 😫, 😀]

// Code
const list = [1, 2, 3, 4, 5];
list.reverse(); // [5, 4, 3, 2, 1]
list; // [5, 4, 3, 2, 1]

Array.sort()

Sorts the elements of an array in place and returns the array. The default sort order is according to string Unicode code points.

const list = [😀, 😫, 😀, 😫, 🤪];
list.sort(); // [😀, 😀, 😫, 😫, 🤪]

// This make more sense 🤔
const array = ['D', 'B', 'A', 'C'];
array.sort(); // 😀 ['A', 'B', 'C', 'D']

// OR
const array = [4, 1, 3, 2, 10];
array.sort(); // 😧 [1, 10, 2, 3, 4]
array.sort((a, b) => a - b); // 😀 [1, 2, 3, 4, 10]

Array.some()

Returns true if at least one element in the array passes the test implemented by the provided function.

const list = [😀, 😫, 😀, 😫, 🤪];
list.some((⚪️) => ⚪️ === 😀); // true
list.some((⚪️) => ⚪️ === 😡); // false

// Code
const list = [1, 2, 3, 4, 5];
list.some((el) => el === 3); // true
list.some((el) => el === 6); // false

Array.every()

Returns true if all elements in the array pass the test implemented by the provided function.

const list = [😀, 😫, 😀, 😫, 🤪];
list.every((⚪️) => ⚪️ === 😀); // false

const list = [😀, 😀, 😀, 😀, 😀];
list.every((⚪️) => ⚪️ === 😀); // true

// Code
const list = [1, 2, 3, 4, 5];
list.every((el) => el === 3); // false

const list = [2, 4, 6, 8, 10];
list.every((el) => el%2 === 0); // true

Array.from()

Creates a new array from an array-like or iterable object.

const list = 😀😫😀😫🤪;
Array.from(list); // [😀, 😫, 😀, 😫, 🤪]

const set = new Set(['😀', '😫', '😀', '😫', '🤪']);
Array.from(set); // [😀, 😫, 🤪]

const range = (n) => Array.from({ length: n }, (_, i) => i + 1);
console.log(range(10)); // [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

Array.of()

Creates a new array with a variable number of arguments, regardless of number or type of the arguments.

const list = Array.of(😀, 😫, 😀, 😫, 🤪);
list; // [😀, 😫, 😀, 😫, 🤪]

// Code
const list = Array.of(1, 2, 3, 4, 5);
list; // [1, 2, 3, 4, 5]

Array.isArray()

Returns true if the given value is an array.

Array.isArray([😀, 😫, 😀, 😫, 🤪]); // true
Array.isArray(🤪); // false

// Code
Array.isArray([1, 2, 3, 4, 5]); // true
Array.isArray(5); // false

Array.at()

Returns a value at the specified index.

const list = [😀, 😫, 😀, 😫, 🤪];
list.at(1); // 😫

// Return from last 🤔
list.at(-1); // 🤪
list.at(-2); // 😫

// Code
const list = [1, 2, 3, 4, 5];
list.at(1); // 2
list.at(-1); // 5
list.at(-2); // 4

Array.copyWithin()

Copies array elements within the array. Returns the modified array.

const list = [😀, 😫, 😀, 😫, 🤪];
list.copyWithin(1, 3); // [😀, 😀, 🤪, 😫, 🤪]

const list = [😀, 😫, 😀, 😫, 🤪];
list.copyWithin(0, 3, 4); // [😫, 😫, 😀, 😫, 🤪]

// Code
const list = [1, 2, 3, 4, 5];
list.copyWithin(0, 3, 4); // [4, 2, 3, 4, 5]

NOTE: 🤔

first argument is the target at which to start copying elements from.
second argument is the index at which to start copying elements from.
third argument is the index at which to stop copying elements from.

Array.flat()

Returns a new array with all sub-array elements concatenated into it recursively up to the specified depth.

const list = [😀, 😫, [😀, 😫, 🤪]];
list.flat(Infinity); // [😀, 😫, 😀, 😫, 🤪]

// Code
const list = [1, 2, [3, 4, [5, 6]]];
list.flat(Infinity); // [1, 2, 3, 4, 5, 6]

Array.flatMap()

Returns a new array formed by applying a given callback function to each element of the array,

const list = [😀, 😫, [😀, 😫, 🤪]];
list.flatMap((⚪️) => [⚪️, ⚪️ + ⚪️ ]); // [😀, 😀😀, 😫, 😫😫, 😀, 😀😀, 😫, 😫😫, 🤪, 🤪🤪]

// Code
const list = [1, 2, 3];
list.flatMap((el) => [el, el * el]); // [1, 1, 2, 4, 3, 9]

Must Read If you haven't

React redux best practice to reduce code

Rahul Sharma ・ May 3 '22

#react #redux #javascript #typescript

How to cancel Javascript API request with AbortController

Rahul Sharma ・ Apr 9 '22

#javascript #webdev #frontend #html

13 Typescript Utility: A Cheat Sheet for Developer

Rahul Sharma ・ Apr 2 '22

#typescript #javascript #webdev #frontend

How to solve REST API routing problem with decorators?

Rahul Sharma ・ Mar 23 '22

#node #typescript #javascript #express

Catch me on

Rahul Sharma

Passionate JavaScript Developer 🚀 | Crafting Web Magic ✨ | Code Enthusiast 💻

Youtube Github LinkedIn Medium Stackblitz Hashnode HackerNoon

28 Javascript Array Methods: A Cheat Sheet for Developer

Array.map()

Returns a new array with the results of calling a provided function on every element in this array.

Array.filter()

Returns a new array with all elements that pass the test implemented by the provided function.

Array.reduce()

Reduce the array to a single value. The value returned by the function is stored in an accumulator (result/total).

Array.reduceRight()

Executes a reducer function (that you provide) on each element of the array resulting in a single output value(from right to left).

Array.fill()

Fill the elements in an array with a static value.

Array.find()

Returns the value of the first element in the array that satisfies the provided testing function. Otherwise undefined is returned.

Array.indexOf()

Returns the first index at which a given element can be found in the array, or -1 if it is not present.

Array.lastIndexOf()

Returns the last index at which a given element can be found in the array, or -1 if it is not present. The array is searched backwards, starting at fromIndex.

Array.findIndex()

Returns the index of the first element in the array that satisfies the provided testing function. Otherwise -1 is returned.

Array.includes()

Returns true if the given element is present in the array.

Array.pop()

Removes the last element from an array and returns that element.

Array.push()

Appends new elements to the end of an array, and returns the new length.

Array.shift()

Removes the first element from an array and returns that element.

Array.unshift()

Adds new elements to the beginning of an array, and returns the new length.

Array.splice()

Changes the contents of an array by removing or replacing existing elements and/or adding new elements in place.

Array.slice()

Returns a shallow copy of a portion of an array into a new array object selected from begin to end (end not included). The original array will not be modified.

Array.join()

Joins all elements of an array into a string.

Array.reverse()

Reverses the order of the elements in an array.

Array.sort()

Sorts the elements of an array in place and returns the array. The default sort order is according to string Unicode code points.

Array.some()

Returns true if at least one element in the array passes the test implemented by the provided function.

Array.every()

Returns true if all elements in the array pass the test implemented by the provided function.

Array.from()

Creates a new array from an array-like or iterable object.

Array.of()

Creates a new array with a variable number of arguments, regardless of number or type of the arguments.

Array.isArray()

Returns true if the given value is an array.

Array.at()

Returns a value at the specified index.

Array.copyWithin()

Copies array elements within the array. Returns the modified array.

Array.flat()

Returns a new array with all sub-array elements concatenated into it recursively up to the specified depth.

Array.flatMap()

Returns a new array formed by applying a given callback function to each element of the array,

Must Read If you haven't

React redux best practice to reduce code

Rahul Sharma ・ May 3 '22

How to cancel Javascript API request with AbortController

Rahul Sharma ・ Apr 9 '22

13 Typescript Utility: A Cheat Sheet for Developer

Rahul Sharma ・ Apr 2 '22

How to solve REST API routing problem with decorators?

Rahul Sharma ・ Mar 23 '22

Catch me on

Rahul SharmaFollow

Rahul Sharma