利用setTimeout和clearTimeout封装setInterval和clearInterval

function SetInterval(fun, sec){
    function recFun(){
        fun();
        this.id = setTimeout(recFun, sec);//将任务的标识符记录在timer对象中
    }
    this.stop = function(){
        clearTimeout(this.id);//取消下一个任务的执行
    }
    this.start = function(){
        if(typeof this.id === "undefined"){
            recFun = recFun.bind(this); //将递归函数的this引用和当前对象即timer绑定
            recFun();
        }
    }
}

/*测试*/
var timer = new SetInterval(() => console.log("?"), 1000);
timer.start();
setTimeout(() => timer.stop(), 5000);