Convert a number in domain A to domain B

normalizer.js

// a normalize function constructor for mapping from one range of numbers to another
// actually it is 4 ranges, one from mid to max another from min to mid for each domain
// so given 3 input (domainA) numbers for min, mid, max
// and given 3 output (domainB) numbers or arrays of any length of numbers also for min, mid, max
// the constructor function will return a normalize function that wil convert any number in domainA to domainB
//
// example:
// 	converting a value from -1 to 1 to a color ramp red to green
// 	with a white neutral in the middle and alpha evenly interpolated
//
// 	example constructor call:
// 		var n = normalizer(-1, 0, 1, [255,0,0,1], [255, 255, 255, 0], [0, 255, 0, 1]);
//
// 	example usage of normalize function:
// 		n(1) -> 	[0, 255, 0, 1]
// 		n(-1) -> 	[255, 0, 0, 1]
// 		n(0) -> 	[255, 255, 255, 0]
// 		n(.5) -> 	[127.5, 255, 127.5, 0.5]
//

normalizer = (function() {
	function _normalize(rangeA, rangeB, xInRangeA) {
		// returns x of a in range of b
		// http://stackoverflow.com/questions/1471370/normalizing-from-0-5-1-to-0-1#answer-17029736
		return ((rangeB[1] - rangeB[0]) * (xInRangeA - rangeA[0]))/(rangeA[1] - rangeA[0]) + rangeB[0];
	}

	return function normalizer(minVal, midVal, maxVal, min, mid, max) {

		return function normalize(val) {
			var rangeA, rangeB;

			if (val > midVal) {
				rangeA = [midVal, maxVal];
				rangeB = [mid, max];
			} else {
				rangeA = [minVal, midVal];
				rangeB = [min, mid];
			}

			if (typeof max == "number") {
				return _normalize(rangeA, rangeB, val);

			} else if (max.map) {
				return rangeB[0].map((v, i) => {
					return _normalize(rangeA, [rangeB[0][i], rangeB[1][i]], val);
				});

			} else {
				throw new Error("Expecting number or array of numbers but saw: " + typeof max)
			}
		};
	};

}());