addEventListener and setInterval fail silently in a Greasemonkey script

Question

I am trying to get code to execute every x amount of time and begin doing so after the page has loaded for the first time, while my debug throws no errors, the script doesn't actually do anything.

So, I am at a bit of a loss and I am thinking it has something to do with the syntax or the way the code is nested. Can you be so kind as to look at my code below and tell me what in the heck I am doing wrong and if there is a better way to fix it?

window.addEventListener('load', function()  {
setInterval(function setTitle(){
    var sInfo = document.getElementById("play_info");
    var iTags = sInfo.innerHTML.split("\">");
    var pTags = iTags[3].split("<");
    document.title = pTags[0];
    return setTitle;
},5000);
});

This is a code inside a Greasemonkey script that will run inside Firefox. Thank you.

Answer 1

Update (Now that target page was given):
The question code did not match the structure of the actual page. It typically would throw TypeError: iTags[3] is undefined errors.

Using DOM methods, to get the desired info, does the job. A working script is:

// ==UserScript==
// @name     _KROQ, song info to page title
// @include  http://betaplayer.radio.com/player/*
// @grant    GM_addStyle
// ==/UserScript==
/*- The @grant directive is needed to work around a design change
    introduced in GM 1.0.   It restores the sandbox.
*/
if (window.top != window.self)  //-- Don't run on frames or iframes.
    return;

window.addEventListener ('load', function () {
    setInterval (setTitle, 5000);
}, false);

function setTitle () {
    var songInfoNode = document.querySelector (
        "#play_info #oflw_shield div.sleeve.hori"
    );
    if (songInfoNode) {
        var songInfoText = songInfoNode.textContent.trim ();

        //console.log ("songInfoText", songInfoText);
        document.title = songInfoText;
    }
}

---

That code is "brittle", but it will work fine on a site that has the structure you seem to expect. However, the only "output" is that the page title might change. That doesn't happen?

One or more of the following is the script's immediate problem:

• The page does not have the structure you are expecting, so the code throws exceptions. You say, "My debug throws no errors". Verify that you checked Firefox's error console, ControlShiftJ, with the display set to "Errors" or to "All".
• Something else in the script, that you are not showing us, is the problem. Include or link to the complete Greasemonkey script.
• The script is operating on <iframe>d content, so changing document.title will have no visible effect. Link to the target page.

For reference, here is more robust version of that code, that also has a console message, so that you can verify operation:

window.addEventListener ('load', function () {
    setInterval (setTitle, 5000);
}, false);

function setTitle () {
    console.log ("Running setTitle()."); 
    var sInfo = document.getElementById ("play_info");
    if (sInfo) {
        var iTags = sInfo.innerHTML.split ("\">");
        if (iTags  &&  iTags.length > 3) {
            var pTags = iTags[3].split ("<");
            if (pTags  &&  pTags.length) {
                document.title = pTags[0];
            }
        }
    }
}

Note that it's not good practice to parse HTML that way, but without seeing the actual target page (or at least the structure of the play_info node), we can't provide a specific alternative.

Answer 2

As Brandon Boone stated, if you are looking for a pure JS solution to find cross-browser solutions for addEventListener, I suggest you use a solution like this.

var e = window.addEventListener ? window.addEventListener : window.attachEvent;
e('load',function(){ ... };