Scale an input number between an input range proportionally down to be in an output range.

scale-range.js

// @flow

/**
 * Scale an input number between an input range proportionally down to be
 * in an output range.
 *
 * @param {number} input - Input number.
 * @param {Array<number, number>} inputRange - The input range.
 * @param {Array<number, number>} outputRange - The output range.
 *
 * @returns {number}
 */
const scaleRange = (
  input: number,
  inputRange: Array<number>,
  outputRange: Array<number>
): number => {
  const [inMin, inMax] = inputRange;
  const [outMin, outMax] = outputRange;

  return ((input - inMin) * (outMax - outMin)) / ((inMax - inMin) + outMin);
};

export default scaleRange;