JavaScript Array Methods Cheat Sheet

• Add to the end
• Use for: adding to cart, appending logs
• Returns: the new array length

const cart = ['apple'];
cart.push('banana'); // 2

• Remove last item
• Use for: undo last action, stack operations
• Returns: the removed item

const stack = ['init', 'save', 'close'];
stack.pop(); // 'close'

• Remove first item
• Use for: processing queues, removing oldest entry
• Returns: the removed item

const queue = ['first', 'second', 'third'];
queue.shift(); // 'first'

• Add to the beginning
• Use for: prepending recent items, priority queues
• Returns: the new array length

const updates = ['old'];
updates.unshift('new'); // 2

• Insert or remove at any position
• Use for: editing lists, removing by index
• Returns: an array of removed items

const list = ['a', 'b', 'c'];
list.splice(1, 1, 'x'); // ['b']

• Copy a section of an array
• Use for: pagination, getting a range
• Returns: a new array copy

const items = ['a', 'b', 'c', 'd'];
const page = items.slice(1, 3); // ['b', 'c']

• Combine arrays
• Use for: combining data from sources
• Returns: a new merged array

const arr1 = [1, 2];
const arr2 = [3, 4];
arr1.concat(arr2); // [1, 2, 3, 4]

• Copy an array
• Use for: copying, combining arrays cleanly
• Returns: a new array

const a = [1, 2];
const b = [...a, 3]; // [1, 2, 3]

• Transform every item
• Use for: formatting prices, extracting props
• Returns: a new transformed array

const prices = [10, 20, 30];
prices.map(p => p * 1.1); // [11, 22, 33]

• Keep matching items
• Use for: search results, showing active users
• Returns: a new filtered array

const users = [{active: true}, {active: false}];
users.filter(u => u.active); // [{active: true}]

• Combine into one value
• Use for: totals, building objects
• Returns: a single value

const nums = [1, 2, 3];
nums.reduce((a, b) => a + b, 0); // 6

• Find first matching item
• Use for: find user by ID
• Returns: the first matching element or undefined

users.find(u => u.id === 1);

• Find index of first match
• Use for: locate item to update
• Returns: the index or -1 if not found

users.findIndex(u => u.id === 1);

• Find index of exact value
• Use for: check simple value
• Returns: the index or -1 if not found

['a', 'b', 'c'].indexOf('b'); // 1

• Check if value exists
• Use for: validating permissions, checking tags
• Returns: a boolean

['read', 'write'].includes('write'); // true

• Any item matches
• Use for: has at least one error, any admin
• Returns: a boolean

users.some(u => u.isAdmin); // true or false

All items match Use for: all fields valid, all tasks complete Returns: a boolean

tasks.every(t => t.done); // true or false

• Sort array in order
• Use for: alphabetizing names, sorting by date
• Returns: the sorted array (same reference)

names.sort((a, b) => a.localeCompare(b));

• Reverse order of array
• Use for: newest first, reverse process
• Returns: the reversed array (same reference)

[1, 2, 3].reverse(); // [3, 2, 1]

• Join array into string
• Use for: CSVs, building URLs
• Returns: a string

['a', 'b', 'c'].join(','); // "a,b,c"

• Run for each item
• Use for: logging, DOM updates
• Returns: undefined

items.forEach(i => console.log(i));

• Convert to array
• Use for: DOM NodeLists, Sets, strings
• Returns: a new array

Array.from('hi'); // ['h', 'i']