LERP - Get from point a to point b over t.

lerp.js

/**
 * Linear interpolation (LERP).
 *
 * Returns a value between value a to value b over t (0 to 1).
 *
 * @param {number} a
 * @param {number} b
 * @param {number} t
 * @returns {number}
 */
function lerp(a, b, t) {
  return a + t * (b - a);
}