用 setTimeout实现setInterval

问题：这个问题是一面试官问的 – 如何用 setTimeout 实现 setInterval 并 clearTimeout

解决办法：

  function Interval(fn, ms){
      return {
          timer_id: null,
          start: function(){
              var that = this;
              if(this.timer_id) { that.clear(); }
              this.timer_id = setTimeout(
                  function(){
                      fn();
                      that.start();
                  }, ms)
          },
          clear: function(){
              clearTimeout(this.timer_id);
          }
      }
  }

  var sum = 0;
  obj = Interval(function(){ console.log(sum++)}, 1000);
  obj.start();  // start interval

  obj.clear(); // clearTimeout