PHP+Ajax implements real-time verification function of verification code

This article mainly introduces in detail the real-time verification of verification code through PHP Ajax. Interested friends can refer to

PHP’s image processing function is powerful, and it is also possible to make a verification code picture. It is very simple, but when implementing real-time verification, I did encounter a problem:
I used nat123 to port map the website on my computer to achieve external network access. Originally, I used cookies to use js to map the website. Verification code was used for verification, but after inspection, it was found that although nat123 allows my website to be accessed through a customized URL, the location of the PHP file that generates the verification code on the network is not in the same domain as other pages. After querying, it was found that Because the output image is mapped in a certain folder as a cache file, so - other pages are under my URL, and the page that generates the verification code is under another URL, so their cookies cannot be shared, regardless of No matter how I set the path and domain, it didn't work, so I had to use the session to store the verification code, because the session exists on the server, which means it can be accessed in my local website.
The next step is the main event. I have only had a rough understanding of ajax before, and I still know its uses and characteristics. However, I don’t know how to start using the relatively general concept of obtaining data from the background.
First of all, I analyzed the code of an example question, which is used to obtain the content of a text file in the background:

function getHTTPObject(){
  if(typedef XMLHttpRequest == "undefined")
    XMLHttpRequest = function(){
      try{ return new ActiveXObject("Msxml2.XMLHTTP.6.0");}
      catch(e){}
      try{ return new ActiveXObject("Msxml2.XMLHTTP.3.0");}
      catch(e){}
      try{ return new ActiveXObject("Msxml2.XMLHTTP");}
      catch(e){}
      return false;
    }
    return new XMLHttpRequest();
}
function getNewContent(){
  var request = getHTTPObject();
  if(request){
    request.open("GET","TEST.txt",true);
    request.onreadystateschange = function(){
      alert(request.responseText);
    }
  }else{
  alert("no support XMLHttpRequest!");
  }
}

The key is:

  request.open("GET","TEST.txt",true);
    request.onreadystateschange =function(){
      alert(request.responseText);
    }

These three sentences specify the page to which the GET request is sent and the processing function that is triggered when the XMLHttpRequest object returns the response, and the data is obtained through request.responseText of.

-------------------------------------------------- ------------------------------------

But the data I want to get is the background How to let the background send the verification code for the verification code generated by the php file?
Regardless of the GET or POST method, data is sent to the background. Where does ajax retrieve the data from the background?
I was puzzled, so I checked another information and found an example:
The processing statement for the response sent back by the XMLHttpRequest object is:

request.onreadystateschange=alertContent;
function alertContent(){
...
  alert(request.responseText);
...
}

The requested file is check.php
There are several conditional output sentences:

if($info){
  echo "你的用户名可以使用";
}else {
  echo "该用户名已被注册";
}

And in the running example renderings Suddenly a message box pops up on the static page, the content is like the output of the check.php page! ! !
That is to say, ajax can request the output content of a php page, so the next step is much simpler. Because the picture is also the output of the verification code page, you cannot directly ajax the verification code page, otherwise the data of the picture will also be obtained. .
Create a new php page:

sission_start();
$code="";
if(!empty($_session['check']))$code=$_session['check'];
echo $code;

Then use ajax to get a request to this page on the front end, and you can use request.responseText to get the verification code.
Then encapsulate the verification process in a function triggered by certain conditions, so that it can be verified in real time.

Summary: The above is the entire content of this article, I hope it will be helpful to everyone's study.

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