The 8 must know JavaScript looping array function

Prima Tondy Arya Kurniawan — Tue, 02 Mar 2021 03:44:09 +0000

Array.map()

Iterate through the array and returning a new value

const array1 = [1, 4, 9, 16];
// pass a function to map
const map1 = array1.map(x => x * 2);
console.log(map1);
// expected output: Array [2, 8, 18, 32]

Array.forEach()

Iterate through the array

const array1 = ['a', 'b', 'c'];
array1.forEach(e=> console.log(e));
// expected output: "a"
// expected output: "b"
// expected output: "c"

Array.every()

Iterate through the array and check every element, return true if every element is right and false if it's not

const array1 = [1, 30, 39, 29, 10, 13];
console.log(array1.every(e => e < 40));
// expected output: true

Array.some()

Iterate through the array and return true if there is one element is right and false if it's not

const array1 = [1, 30, 39, 29, 10, 13];
console.log(array1.some(e => e < 10));
// expected output: true

Array.find()

Iterate through the array and return the first element if it's true and undefine if there is no the right element

const array1 = [5, 12, 8, 130, 44];
const found = array1.find(e=> e> 10);
console.log(found);
// expected output: 12

Array.findIndex()

Iterate through the array and return the index of first element if it's true and -1 if there is no the right element

const array1 = [5, 12, 8, 130, 44];
const found = array1.find(e=> e> 10);
console.log(found);
// expected output: 1

Array.sort()

Sort and array through every element, return a ascending order array if the result is greater then 0 and descending if the result is lesser then 0;

let numbers = [4, 2, 5, 1, 3];
numbers.sort((a, b) => a - b);
console.log(numbers);
// [1, 2, 3, 4, 5]

Array.reduce()

A reducer function on each element of the array, resulting in single output value.

const array1 = [1, 2, 3, 4];
// 1 + 2 + 3 + 4
console.log(array1.reduce((accumulator, currentValue) => accumulator + currentValue));
// expected output: 10

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