Error using ajax to send JSON data to a private server

Question

I am pretty new to writing userscripts for Chrome/Firefox. I was trying to get the AJAX generated JSON data from a website and send them to my own server, to analyze them and put them into a database.

I managed to send the data with Ajax and put them into a text file on my own server. But in the Chrome Console it says that I have:

Uncaught SyntaxError: Unexpected token j

, but I already have got each message, that 'Data were sent' and that I'm 'After the call' -those are the logging messages.

Is there a callback, that I should implement, or am I missing something obvious? I am putting a shortened version of my code up here.

// Injecting javascript in the original page
function inject(func) {
    var source = func.toString();
    var script = document.createElement('script');
    script.innerHTML = "(" + source + ")()";
    document.body.appendChild(script);
}

function injection() {
}

// This function intercepts the ajax
function interceptAjax() {
    $('body').ajaxSuccess (
            function (event, requestData, settings) {
                serverData = requestData.responseText;

                if(JSON.parse(settings.data).method == "dashboard.getPaginatedPlextsV2"){

                console.log("Sending");
                $.ajax({
                    type: "POST",
                    url: "http://mywebsite.com/collectdata.php",
                    data: { json: JSON.stringify(serverData) },
                    success: function(msg) {
                        console.log("Data were sent");
                    },
                    error: function(xhr, ajaxOptions, thrownError) {
                        console.log("Failed: " + xhr.status + " - " + thrownError);
                    }
                });

                console.log("After the call");
                }
            }
    );
}

// A helperfunction for the ajaxInterception to work in Chrome
function addJS_Node (text, s_URL, funcToRun) {
    var D = document;
    var scriptNode = D.createElement('script');
    scriptNode.type = "text/javascript";
    if(text) scriptNode.textContent = text;
    if(s_URL) scriptNode.src = s_URL;
    if(funcToRun) scriptNode.textContent = '(' + funcToRun.toString() + ')()';

    var targ = D.getElementsByTagName('head')[0] || D.body || D.documentElement;
    targ.appendChild(scriptNode);
}

// This function is necessary to intercept the ajax
addJS_Node(null, null, interceptAjax);

inject(injection);

Answer 1

Couple things:

1. Is mywebsite.com the same domain as the target page? If not, then you can't do cross-domain AJAX like that (unless the target-page server has a generous CORS policy).

   If so, then you control the server (or have access), so why mess about with a userscript for the data? ;-)

2. This line:

   if(JSON.parse(settings.data).method == "dashboard.getPaginatedPlextsV2")
   

   looks prone to cause errors.

Even if you are reasonably sure that all of the page's AJAX calls send only valid JSON data, not all of the data will have a method property. (EG: it looks like the AJAX call to http://mywebsite.com/collectdata.php might not have one.

You need to make that check a little more crash-resistant. Something like this (untested):

var jsonData    = null;

try {
    jsonData    = JSON.parse (settings.data);
}
catch (e) {
    jsonData    = null;
}

if (jsonData  &&  jsonData.method
    &&  jsonData.method == "dashboard.getPaginatedPlextsV2"
) {
    ...