Javascript - How to detect if document has loaded

Question

I want to call a function after a document loads, but the document may or may not have finished loading yet. If it did load, then I can just call the function. If it did NOT load, then I can attach an event listener. I can't add an eventlistener after onload has already fired since it won't get called. So how can I check if the document has loaded? I tried the code below but it doesn't entirely work. Any ideas?

var body = document.getElementsByTagName('BODY')[0];
// CONDITION DOES NOT WORK
if (body && body.readyState == 'loaded') {
    DoStuffFunction();
} else {
    // CODE BELOW WORKS
    if (window.addEventListener) {  
        window.addEventListener('load', DoStuffFunction, false);
    } else {
        window.attachEvent('onload', DoStuffFunction);
    }
}

Answer 1

if(document.loaded) {
    DoStuffFunction();
} else {
    if (window.addEventListener) {  
        window.addEventListener('load', DoStuffFunction, false);
    } else {
        window.attachEvent('onload', DoStuffFunction);
    }
}

Answer 2

Mozila Firefox says that onreadystatechange is an alternative to DOMContentLoaded.

// alternative to DOMContentLoaded
document.onreadystatechange = function () {
    if (document.readyState == "complete") {
        initApplication();
    }
}

In DOMContentLoaded the Mozila's doc says:

The DOMContentLoaded event is fired when the document has been completely loaded and parsed, without waiting for stylesheets, images, and subframes to finish loading (the load event can be used to detect a fully-loaded page).

I think load event should be used for a full document+resources loading.

Answer 3

There's no need for all the code mentioned by galambalazs. The cross-browser way to do it in pure JavaScript is simply to test document.readyState:

if (document.readyState === "complete") { init(); }

This is also how jQuery does it.

Depending on where the JavaScript is loaded, this can be done inside an interval:

var readyStateCheckInterval = setInterval(function() {
    if (document.readyState === "complete") {
        clearInterval(readyStateCheckInterval);
        init();
    }
}, 10);

In fact, document.readyState can have three states:

Returns "loading" while the document is loading, "interactive" once it is finished parsing but still loading sub-resources, and "complete" once it has loaded. -- document.readyState at Mozilla Developer Network

So if you only need the DOM to be ready, check for document.readyState === "interactive". If you need the whole page to be ready, including images, check for document.readyState === "complete".