AJAX Server loopback data failed onreadystatechange cannot trigger callback function

AJAX Server loopback data failed onreadystatechange cannot trigger callback function
Enter an e-mail message in a text label that triggers a validation event when onblur, to the database to verify that the user already exists, where the Dispear method is the method that is triggered by the onblur event. Verified the server has received the data sent locally and verified the success, but Echo does not go back.
The JS code is as follows:
var myxmlhttprequest;
function Getxmlhttpobject () {
var XMLHttpRequest;
try{
Xmlhttprequest=new XMLHttpRequest ();

}
catch (e) {
try{
Xmlhttprequest=new ActiveXObject ("msxml2.hmlhttp");

}
catch (e) {
Xmlhttprequest=new ActiveXObject ("Microsoft.XMLHTTP");

}
}
return XMLHttpRequest;
}




function isexist (email) {

Myxmlhttprequest=getxmlhttpobject ();
if (myxmlhttprequest) {
Alert ("Hello" +email);

var url= "/renren/register_legal_process.php";
var data= "email=" +email;
Myxmlhttprequest.open ("Post", url,true);
Myxmlhttprequest.setrequestheader ("Content-type", "application/x-www-form-urlencoded");
Specifying a callback function


Myxmlhttprequest. Onreadystatechange=deal;
Myxmlhttprequest.send (data);

alert (myxmlhttprequest.readystate);
}
}
Function Deal () {

Alert (' Hello ');
if (myxmlhttprequest.readystate==4) {

var Isexist=myxmlhttprequest.responsetext;

if (isexist== "exist") {
$ ("Focus1"). style.display= "None";
$ ("Wrong1"). style.display= "None";
$ ("Duihao"). style.display= "None";
$ (' Wrong5 '). style.display= "Block";
}else if (isexist== "Notexist") {
$ ("Focus1"). style.display= "None";
$ ("Wrong1"). style.display= "None";
$ ("Wrong5"). style.display= "None";
$ ("Duihao"). style.display= "Block";
}


}

}
function $ (ID) {
return document.getElementById (ID);
}
function disappear (REF1,REF2,REF3,REF4) {
var app=$ (REF1);
var tmp1=$ (REF2);
var tmp2=$ (REF3);
var tmp3=$ (REF4);
var Str=tmp1.value;
var reg=/^ ([a-za-z0-9]+[_|\-|\.]?) *[a-za-z0-9]+@ ([a-za-z0-9]+[_|\-|\.]?) *[a-za-z0-9]+\. [A-za-z] {2,3}$/gi;

if (!reg.test (str))
{
Tmp3.style.display= "None";
App.style.display= "None";
$ ("Wrong5"). style.display= "None";
Tmp2.style.display= "";
}
Else
{
/*
* tmp2.style.display= "None"; App.style.display= "None";
* tmp3.style.display= "";
*/

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