Step 2 – "There you go!"
or Handling the Server Response
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Remember that when you were sending the request, you provided the name of a JavaScript function that is designed to handle the response.

http_request.onreadystatechange = nameOfTheFunction;

Let's see what this function should do. First, the function needs to check for the state of the request. If the state has the value of 4, that means that the full server response is received and it's OK for you to continue processing it.

if (http_request.readyState == 4) {
    // everything is good, the response is received
} else {
    // still not ready

The full list of the readyState values is as follows:


The next thing to check is the status code of the HTTP server response. All the possible codes are listed on the W3C site. For our purposes we are only interested in 200 OK response.

if (http_request.status == 200) {
    // perfect!
} else {
    // there was a problem with the request,
    // for example the response may be a 404 (Not Found)
    // or 500 (Internal Server Error) response codes

Now after you've checked the state of the request and the HTTP status code of the response, it's up to you to do whatever you want with the data the server has sent to you. You have two options to access that data:

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