Possible HTTP Request states after form submit

Question

I'm trying to submit a form and get the results inpage using AJAX. I call a JS function onsubmit which makes the AJAX call, and includes this code:

        request=new XMLHttpRequest();
        /* set up request here */
        request.onreadystatechange=function() {
        if (request.readyState == 4 && request.status == 200) {
            /* do what I need */
            alert('Success');
        } else {
            /* do what I need */
            alert('Failed');
        }
    }

However, the Failed alert shows up multiple times (3 at least) before the Success one, so I guess I'm getting many different statuses before the successful one? How can I check which ones I get, and what to expect when the submission is failed? Thanks.

Answer 1

You only ever get one status, but you get multiple states .

Check to see if the readyState is 4 or 0 (since either of those states indicate that there is no more of the response to wait for).

Then throw an error if it is 0 or test the status if it is 4 .

If the readyState is any other value, then ignore it (unless you want to do stuff in other states).

Answer 2

The request goes through four phases. The readyStates. Every time the readystate updates it fires the event. 0 indicates a failure and 4 indicates that the request has finished. the status returns the http code. 200 indicates success. There was an answer and it returned a request body . All other codes indicate there was something wrong on the server side. Eg. 404, 403, or 500. You can safely ignore the other readystates . But catch any status other than 200 as failure.