Xmlhttprequest Launches Multiple Times Without Initiating The Onreadystatechange Function

The userscript in question: http://userscripts.org/scripts/show/130532 After the site it's been made for has been updated to HTML5, I had to update the script. However, it's got a

Solution 1:

You're using several variables without declaring these locally:

var ..., found, xhr1, xhr2, cstatus, ui, pg;
...
functiondoIndex(pg) {
    ...
        xhr1 = newXMLHttpRequest();
     // ^^^^ No var !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
        ...
        xhr1.onreadystatechange = function() {
            if (xhr1.readyState === 4) { ... }
            if (found) {
                ...
            } else {
                if (pg < 15) {
                    doIndex(pg + 1); // <-- !!!!!!!!!!!!!!!!!!
                } else { ...
                    xhr2 = newXMLHttpRequest();
                    ...
                    xhr2.onreadystatechange = function() { ... };
                    xhr2.send(null);
                }
            }
        };
        xhr1.send(null);
    }
}  ...
doIndex(0); // Initiate the doom

First, you assign a new XHR instance to a non-local xhr1 variable. Then, you add a readystatechange event handler, in which the following happens:

1. Initially, readyState is not four, so found is false. Since pg starts at 0, doIndex(pg + 1) is called. Now, xhr1 gets overwritten by a new XHR instance.
2. This continues, until pg reaches 15. Then, pg < 15 is false, and the horror starts:
   • xhr1.onreadystatechange fires multiple time during the request. pg < 15 is false, so the else block is evaluated, in which you launch several new XHR (xhr2) requests...
   • All of the previous readystatechange events are still fired, because the requests haven't finished yet. In every event handler, you're comparing the value of xhr1.readyState, which refers to the state of the last created xhr1 request. So, you're calling doIndex(pg+1) over and over again, which, once pg has reached 15, creates new XHR (xhr2) instances.

To fix the problem, declare the variables in the function, and wrap the whole onreadystatechange block in if (xhr1.readyState == 4) (or use onload instead of onreadystatechange).

functiondIndex(pg) {
    var xhr1, xhr2;
    ...
    xhr1.onreadystatechange = function() {
        if (xhr1.readyState === 4) {
           /* ... */
        }
    };
    ...

Solution 2:

This helped based on answers:

                    let signupRequest = new XMLHttpRequest();
                    let url = "signup/" + inputMobile.value;
                    signupRequest.open("GET", url, true);
                    signupRequest.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
                    signupRequest.send();

                    signupRequest.onreadystatechange = function() {
                        if (signupRequest.readyState === 4) {
                            hideLoading();
                            if (signupRequest.status === 200) {
                                console.log("OK: " + status + " --- " + signupRequest.response);
                            } else {
                                console.log("NOK: " + status + " --- " + signupRequest.response);
                            }
                        }
                    };