单方向指定时间内的匀速运动

  /**
   * @param    {[type]}   start   [开始位置]
   * @param    {[type]}   alter   [改变的距离]
   * @param    {[type]}   curTime [已运行的时间]
   * @param    {[type]}   dur     [总时间]
   * @return   {[type]}           [返回当前时间的所在位置]
   */
  function linear(start, alter, curTime, dur) {
    return start + alter / dur * curTime;
  }

  var start = 10,
    target = 20,
    dur = 500;
  var alter = target - start,
    curTime = 0;
  var y = 0;
  // interval  影响curTime值
  var interval = 11;

  var timer = window.setInterval(animate, interval);
  function animate () {
      curTime += interval;
      y = linear(start, alter, curTime, dur);
      console.log(y);
      if (y >= target) {
          y = target;
          box.style.left = y + "px";
          window.clearInterval(timer);
          timer = null;
          return;
      }
      box.style.left = y + "px";
  }

  var timer = window.setTimeout(animate, interval);
  function animate () {
      window.clearTimeout(timer);
      curTime += interval;
      y = linear(start, alter, curTime, dur);
      console.log(y);
      if (y >= target) {
          y = target;
          box.style.left = y + "px";
          timer = null;
          return;
      }
      box.style.left = y + "px";
      timer = window.setTimeout(animate, interval);
  }

  function animate() {
    window.clearTimeout(timer);
    way = way || linear;
    y = way(start, alter, curTime, dur);
    // 这里开始判断target和start的大小
    if (target = start) {
      return;
    }
    if (target > start) {
      curTime += interval;
      y >= target && afterTarget();
    } else if (target > start) {
      curTime -= interval;
      y <= target && afterTarget();
    } else {
      return;
    }

    console.log(y);
    // 超出范围之后,清除定时器,重置属性
    function afterTarget() {
      y = target;
      // 加单位,这里默认加px,如果是别的,加第二个参数即可
      ele.style[attr] = addPx(y);
      timer = null;
      return;
    }

    ele.style[attr] = addPx(y);
    timer = window.setTimeout(animate, interval);
  }