用setTimeout模拟setInterval的功能

偶然看到这个题目，稍微写了下，做个笔记，不足之处请指正

//用setTimeout模仿setInterval
var MyInterVal = function(fun,tm){
    if(this == window){
        return new MyInterVal(fun,tm);
    }
　　this.Fun = null;
    this.id = -1;this.clear = function(id){
        clearTimeout(this.id);
    }
    this.setInterval = function(_fun,_tm){
        var self = this;
        if(this.Fun==null){
            if(typeof _fun=="string"){
                this.Fun = new Function(_fun);
            }else if(typeof _fun=='function'){
                this.Fun = _fun;
            }
        }
        this.id = setTimeout(function(){
            self.Fun();
            self.setInterval(self.Fun,_tm);
        },tm);
    }
    this.setInterval(fun,tm);
}

//使用方法一
var s = MyInterVal(function(){
    console.log(1);
},1000);

//使用方法二
var s = MyInterVal("console.log(1)",1000)

setTimeout(function(){
    s.clear();//清除
},5000)