Javascript – How to get the difference between two arrays in JavaScript

array-differencearraysjavascript

Is there a way to return the difference between two arrays in JavaScript?

For example:

var a1 = ['a', 'b'];
var a2 = ['a', 'b', 'c', 'd'];

// need ["c", "d"]

Best Answer

There is a better way using ES7:


Intersection

 let intersection = arr1.filter(x => arr2.includes(x));

Intersection difference Venn Diagram

For [1,2,3] [2,3] it will yield [2,3]. On the other hand, for [1,2,3] [2,3,5] will return the same thing.


Difference

let difference = arr1.filter(x => !arr2.includes(x));

Right difference Venn Diagram

For [1,2,3] [2,3] it will yield [1]. On the other hand, for [1,2,3] [2,3,5] will return the same thing.


For a symmetric difference, you can do:

let difference = arr1
                 .filter(x => !arr2.includes(x))
                 .concat(arr2.filter(x => !arr1.includes(x)));

Symmetric difference Venn Diagram

This way, you will get an array containing all the elements of arr1 that are not in arr2 and vice-versa

As @Joshaven Potter pointed out on his answer, you can add this to Array.prototype so it can be used like this:

Array.prototype.diff = function(arr2) { return this.filter(x => !arr2.includes(x)); }
[1, 2, 3].diff([2, 3])