Javascript Map range of number to another range

map.js

Number.prototype.map = function (in_min, in_max, out_min, out_max) {
  return (this - in_min) * (out_max - out_min) / (in_max - in_min) + out_min;
}

map.ts

export function clamp(input: number, min: number, max: number): number {
  return input < min ? min : input > max ? max : input;
}

export function map(current: number, in_min: number, in_max: number, out_min: number, out_max: number): number {
  const mapped: number = ((current - in_min) * (out_max - out_min)) / (in_max - in_min) + out_min;
  return clamp(mapped, out_min, out_max);
}

For float values at least, this method doesn't work. It can actually go slightly above. This is the correct function to deal with floats

(Number as any).prototype.map = function (in_min, in_max, out_min, out_max) {
	let val = (this - in_min) * (out_max - out_min) / (in_max - in_min) + out_min;
	if (val < out_min) val = out_min;
	else if (val > out_max) val = out_max;
	return val;
}

@marcusx2 Since you added (Number as any) I updated the snippet and add a typescript version to reflect what I currently use in production

If you use GSAP, it has this as one of its utility methods as gsap.utils.mapRange. I haven't quite tested out how it deals with cases like floats. Also, I like that GSAP's mapRange has a handy feature that makes it return a function that 'remembers' the in_min, in_max, etc., values so that you can pass in any number input to repeat calculations with the same ranges.

simpler version:

const lerp = (a, b, t) => (b-a)*t+a;
const unlerp = (a, b, t) => (t-a)/(b-a);
const map = (a1, b1, a2, b2, t) => lerp(a2, b2, unlerp(a1, b1, t));

@mekb-turtle What does lerp mean?

@mekb-turtle What does lerp mean?

Linear Interpolation