How to Get Intersection of Two Arrays in JavaScript

To get the difference of two arrays in JavaScript, you can use the combination of filter and includes. Imagine you have the following two arrays and you want to find out which elements are included in both:

const veggies = ['🍅', '🥕', '🥒'];
const fruits  = ['🍓', '🍌', '🍅'];

To get their intersection, you can use the following call:

const intersection = veggies.filter(v => fruits.includes(v));

To get their differencem eg.: only the ones that veggies include, you can do the following:

const difference = veggies.filter(v => !fruits.includes(v));
const difference = fruits.filter(f => !veggies.includes(f));

And in order to get the symmetric difference of two arrays — meaning leave out the ones that are in both arrays — you need to filter both of them and either use concat or destructuring:

const symmetricDifference = [
    ...veggies.filter(v => !fruits.includes(v)),
    ...fruits.filter(f => !veggies.includes(f))
];

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Reusable functions

If you need to rely on the same logic multiple times in your codebase, you can reuse them with the following function calls:

const intersect  = (a, b) => a.filter(a => b.includes(a));
const difference = (a, b) => a.filter(a => !b.includes(a));
const symmetric  = (a, b) => [
    ...a.filter(a => !b.includes(a)),
    ...b.filter(b => !a.includes(b))
];

Why Do You Need to Know About Functional Programming?The programming paradigm that simplifies your codeJust like object-oriented programming, functional programming has its own concepts too. Learn how you can apply them to JavaScript to make your code better.Learn More

Resources:

• Array.prototype.filter
• Array.prototype.includes