Javascript Array Methods Cheatsheet

Here's a cheatsheet of some common JavaScript array methods:

• Array.prototype.push([item1, ..., itemN]) Adds one or more elements to the end of an array and returns the new length of the array.

 let arr = [1, 2, 3]; arr.push(4); 

Results: [1, 2, 3, 4]

• Array.prototype.pop() Removes the last element from an array and returns that element.

 let arr = [1, 2, 3, 4]; let lastItem = arr.pop(); 

Results: 4 (lastItem), [1, 2, 3] (arr)

• Array.prototype.shift() Removes the first element from an array and returns that removed element.

 let arr = [1, 2, 3, 4]; let firstItem = arr.shift(); 

Results: 1 (firstItem), [2, 3, 4] (arr)

• Array.prototype.unshift([item1, ..., itemN]) Adds one or more elements to the beginning of an array and returns the new length of the array.

 let arr = [1, 2, 3]; arr.unshift(0); 

Results: [0, 1, 2, 3]

• Array.prototype.slice([start?, end?]) Returns a shallow copy of a portion of an array into a new array object selected from start to end (end not included).

 let arr = [1, 2, 3, 4]; let subArr = arr.slice(1, 3); 

Results: [2, 3] (subArr)

• Array.prototype.splice(start, deleteCount, [item1, ..., itemN]) Changes the contents of an array by removing or replacing existing elements and/or adding new elements in place.

 let arr = [1, 2, 3, 4]; arr.splice(1, 2, 'a', 'b'); 

Results: [1, 'a', 'b', 4]

• Array.prototype.sort([compareFunction]) Sorts the elements of an array in place and returns the array.

 let arr = [3, 1, 4, 1]; arr.sort(((a, b) => a - b)); 

Results: [1, 1, 3, 4]

• Array.prototype.reverse() Reverses an array in place.

 let arr = [1, 2, 3, 4]; arr.reverse(); 

Results: [4, 3, 2, 1]

• Array.prototype.indexOf(searchElement[, fromIndex]) Returns the first index at which a given element can be found in the array, or -1 if it is not present.

 let arr = [1, 2, 3, 4]; let index = arr.indexOf(3); 

Results: 2 (index)

• Array.prototype.includes(searchElement[, fromIndex]) Determines whether an array includes a certain value among its entries, returning true or false as appropriate.

 let arr = [1, 2, 3, 4]; let hasThree = arr.includes(3); 

Results: true (hasThree)

• Array.prototype.filter(callback[, thisArg]) Creates a new array with all elements that pass the test implemented by the provided function.

 let arr = [1, 2, 3, 4]; let isEven = arr.filter(num => num % 2 === 0); 

Results: [2, 4] (isEven)

• Array.prototype.map(callback[, thisArg]) Creates a new array with the results of calling a provided function on every element in the calling array.

 let arr = [1, 2, 3, 4]; let squares = arr.map(num => num * num); 

Results: [1, 4, 9, 16] (squares)

• Array.prototype.reduce(callback[, initialValue]) Apply a function against an accumulator and each element in the array (from left to right) to reduce it to a single output value.

 let arr = [1, 2, 3, 4]; let sum = arr.reduce((acc, num) => acc + num, 0); 

Results: 10 (sum)