JavaScript Arrays Cheat Sheet

1. Iteration Methods (Modern ES6)

The best ways to loop through array elements cleanly.

Array.prototype.forEach()

Executes a provided function once for each array element. Does not return a new array.

const numbers = [1, 2, 3];
numbers.forEach(num => console.log(num)); // 1, 2, 3

Array.prototype.map()

Creates a new array populated with the results of calling a provided function on every element.

const numbers = [1, 2, 3];
const doubled = numbers.map(num => num * 2);
// doubled is [2, 4, 6]

Array.prototype.filter()

Creates a shallow copy containing only elements that pass the test implemented by the provided function.

const ages = [12, 18, 24, 7];
const adults = ages.filter(age => age >= 18);
// adults is [18, 24]

2. Mutating Arrays

Methods that change the array in place.

• push(items): Adds one or more elements to the end of an array.
• pop(): Removes the last element from an array.
• shift(): Removes the first element from an array.
• unshift(items): Adds one or more elements to the front of an array.
• splice(start, count, items): Changes the contents of an array by removing or replacing existing elements and/or adding new elements.

3. Searching Arrays

Quickly find items within your arrays.

• find(callback): Returns the first element that satisfies the testing function.
• findIndex(callback): Returns the index of the first element that satisfies the test.
• includes(value): Determines whether an array includes a certain value (returns boolean).
• indexOf(value): Returns the first index at which a given element can be found, or -1 if it is not present.