A Quick Guide to Clamping Numbers in JavaScript

In JavaScript, there's "Math.min()", "Math.max()", but unfortunately no Math.clamp(). There's a proposal for this, but it's currently in the draft stages. This is fine - it's very easy to implement clamp, and in this article, I'll talk through doing just that.

A Quick Way.

You can use the following function to clamp a number between a minimum and maximum value:

function clamp(num: number, lower: number, upper: number) {
    return Math.min(Math.max(num, lower), upper);
}

Why does this work? Let's think it through. At first our number is any valid JavaScript number, anything in the range -Number.MAX_VALUE <= num <= Number.MAX_VALUE

Then we have:

Math.max(num, lower);

So now our range gets updated to whatever the larger value is out of "lower" and "num". Our range is now: lower <= num <= Number.MAX_VALUE.

I'm sure you can see where this is going - let's break our code up:

const lowerBound = Math.max(num, lower);
const result = Math.min(lowerBound, upper);

Just like before but reversed. Our result is the lower of num or upper, so we can update our range to: lower <= num <= upper.

And just like that, our number is clamped! If it's lower than the lower bound, we pick the lower bound. If it's higher than the upper bound, we pick the upper bound. Otherwise, we pick the number.

Lodash.

Lodash is a JavaScript utility library. You can install it with one of these commands:

npm i lodash
pnpm add lodash
yarn add lodash

And it works exactly the same as our function:

import { clamp } from 'lodash';
clamp(number, lower, upper);

Short and simple! If you're not familiar with Lodash, it can be quite handy if you're looking for any functions not native to JavaScript. Check it out here.

Conclusion.

So there's two ways of getting the clamp math function into your JavaScript code. Which one should you use? Personally, I think since it's such a small function, you should probably just implement this one yourself if you need it. If you're already using Lodash though, then you may as well use their built-in function. Thanks for reading! If you liked this article, why not follow me on Twitter?