var i=0;
var int=self.setInterval(function(){
console.log(i++);
change_img();
},20);

clearInterval(int); //停止定时器

      var isclick = true;
        function post_test() {
            if (isclick) {
                isclick = false;
                //---
                var posturl = "/Home/P_Getcode";
                var formData = new FormData();
                myxhr.mypost(posturl, ‘json‘, formData, callback_1);
                //---
                setTimeout(function () {
                    isclick = true;
                }, 500);
            }
        }