Greasemonkey script not working

Question

Here is the full Greasemonkey script to remove a model screen/page that pops-up or blocks the actual web content when the adblocker is enabled in firefox. But its not removing the model screen.

/**

// ==UserScript==
// @name        test
// @namespace   test
// @include     *
// @version     1
// @grant       none
// ==/UserScript==


if (document.getElementsByClassName('tmask')[0]) {
    document.getElementsByClassName('tmask')[0].style.display = 'none';
    document.getElementsByClassName('tbox')[0].style.display = 'none';
}

**/

However when the modal page pop-up and if I open the "Web Developer > Web Console" and execute these lines

if (document.getElementsByClassName('tmask')[0]) {
    document.getElementsByClassName('tmask')[0].style.display = 'none';
    document.getElementsByClassName('tbox')[0].style.display = 'none';
}

It works i.e it removes the modal webpage and lets me read the web contents.

Any help is appreciated. Let me know if more information is needed.

Answer 1

var interval;

function go()
{
     if (document.getElementsByClassName('tmask')[0]) {
        document.getElementsByClassName('tmask')[0].style.display = 'none';
        document.getElementsByClassName('tbox')[0].style.display = 'none';
        clearInterval(interval);
     }
}

window.addEventListener( 'load', function( event )
{
    if( window.top == window.self ) //don't run in frames
    {
        interval = setInterval( go, 500 );
    }
}, false );

My guess is you're not waiting for the page to load, thus your script runs before 'tmask' actually exists.