simpleTween.js

(() => {
  const rAF = window.requestAnimationFrame
    ? window.requestAnimationFrame.bind(window)
    : callback => window.setTimeout(callback, 16);
  const getNow = () => new Date().getTime();

  const tween = ({ duration = 1000 } = {}) => {
    const start = ({ update, complete } = {}) => {
      const play = () => {
        if (duration <= 0) return;

        const now = getNow();
        const elapsedTime = Math.min(duration, now - startTime);
        if (elapsedTime >= duration) {
          update && update(1);
          complete && complete({ startTime, now, elapsedTime });
        } else {
          const range = elapsedTime / duration;
          update && update(range);
          rAF(play);
        }
      };

      const startTime = getNow();
      play();
    };

    return {
      start
    };
  };
  tween.version = "0.0.1";
  window.simpleTween = tween;
})();

// const log = console.log.bind(console);
// window.simpleTween({ duration: 500 }).start({ update: log, complete: log });