手机验证60s后重发问题？要清除定时

var countdown = 60;  
            function timedown(obj) {  
                if (countdown == 0) {  
                    obj.removeAttribute("disabled");  
                    obj.value = "获取验证码";  
                    return clearTimeout();//清除定时，没有的话会导致后面每次减一越来越快  
                } else {  
                    obj.setAttribute("disabled", true);  
                    obj.value = "重新发送(" + countdown + ")";  
                    countdown--;  
                }  
                setTimeout(function() {  
                        timedown(obj);  
                    }, 1000);//定时每秒减一  
            }  
            //手机验证,判断60s之后再发送验证码  
            function settime(obj) {  
                var reg_phone_number = document.getElementById("reg_phone_number");  
                var reg_getcode = document.getElementById("reg_getcode");  
                var check_phone_number = /^1[3458]\d{9}$/;  
                if (reg_phone_number.value.length == 0) {  
                    plus.ui.toast("手机号不能为空");  
                    return;  
                }  
                if (reg_phone_number.value.length != 11) {  
                    plus.ui.toast("请输入有效的手机号！");  
                    return;  
                }  
                if (!reg_phone_number.value.match(check_phone_number)) {  
                    plus.ui.toast("请输入有效的手机号");  
                    return;  
                } else {  
                                        //短信发送  
                    /*                  var url = strWebServer + "/App_Fun/Login/Reg_Edit.ashx";  
                                        var _params = {  
                                            config: {  
                                                action: "getCode",  
                                                strTel: reg_phone_number.value  
                                            },  
                                            fun_Success: function(data) {  
                                                if (data.success == "true") {  
                                                    plus.ui.toast("短信已发送");  
                                                } else {  
                                                    plus.ui.toast(data.msg);  
                                                }  
                                            }  
                                        };  
                                        fun_ExcuteAjax(url, _params);*/  
                    countdown = 5;  
//                  alert("haha");//用于测试  
                    timedown(obj);  
                }  
            }