Below are some of the most commonly used JavaScript array methods. It’s helpful to understand what each method returns and whether the method modifies the original array.

myArray.push(); adds new element to end of array:

var arr = ["a", "b", "c"];

arr.push("d")); 

console.log(arr); // ["a", "b", "c", "d"] (modifies the original array)

myArray.pop(); removes last element in array and returns that element:

var arr = ["a", "b", "c", "d"];

console.log(arr.pop()); // d

console.log(arr); // ["a", "b", "c"] (modifies the original array)

myArray.concat(); concatenates two arrays:

var arrOne = ["a", "b"];

var arrTwo = ["c", "d"];

console.log(arrOne.concat(arrTwo)); // ["a", "b", "c", "d"]

console.log(arrOne); // ["a", "b"] (does not modify original array)

console.log(arrTwo); // ["c", "d"] (does not modify original array)

myArray.join(); joins all elements of array to create a string:

var arr = ["a", "b", "c", "d"];

console.log(arr.join("")); // abcd

console.log(arr); // ["a", "b", "c", "d"]  (does not modify original array)

myArray.reverse(); reverses the elements in an array:

var arr = ["a", "b", "c", "d"];

console.log(arr.reverse()); // ["d", "c", "b", "a"] 

console.log(arr); // ["d", "c", "b", "a"] (modifies the original array)

myArray.shift(); removes the first element in array and returns the last element:

var arr = ["a", "b", "c"];

console.log(arr.shift()); // a (removes and returns the first element)

console.log(arr); // ["b", "c"] (modifies the original array)

myArray.unshift(); adds new elements to beginning of array and returns the length of the modified array:

var arr = ["a", "b", "c"];

console.log(arr.unshift("d")); // 4 (retuns the number of elements after item added)

console.log(arr); // ["d", "a", "b", "c"]  (modifies the original array)

myArray.sort(); sorts an array:

var arr = ["d", "b", "c", "a"];

console.log(arr.sort()); // ["a", "b", "c", "d"] (retuns sorted array)

console.log(arr); // ["a", "b", "c", "d"] (modifies the original array)

myArray.slice(); selects part of an array and returns a new array. The original array remains unchanged. .slice() accepts two arguments: (1) start and (2) end-1. For example:

var arr = ["a", "b", "c"];

console.log(arr.slice(1,2)); // ["b"]

console.log(arr); // ["a", "b", "c"]  (does not modify original array)

myArray.splice(); adds or removes elements from array and returns a new array. The original array is modified. .splice() takes at least two arguments: (1) start and (2) number of items to count from starting point. If the second argument is set to 0, no items will be removed. Items can also be added to the array by including them as additional arguments. For example:

var arr = ["a", "b", "c"];

console.log(arr.splice(1,2)); // ["b", "c"] (returns what was removed)

console.log(arr); // ["a"] (modifies the original array)

var fruitArr = ["apple", "orange", "banana"];

console.log(fruitArr.splice(1,0,"peach")); // [] (returns empty array because nothing was removed)

console.log(fruitArr); // ["apple", "peach", "orange", "banana"]  (modifies original array by adding "peach" in the 1 position)

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Koren Leslie Cohen

Product manager at Facebook. Former senior product manager at Dollar Shave Club in Los Angeles and software engineer at J.Crew / Madewell in New York City. Recovering trial lawyer.

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