How to detect if DOMContentLoaded was fired

Question

I\'m trying to help developing a library and for it I\'m trying to work with page loading.
In the process I want to make the library completely compatible with the use o

Answer 1

For seeing if all resources in the page have been loaded:

if (document.readyState === "complete" || document.readyState === "loaded") {
     // document is already ready to go
}

This has been supported in IE and webkit for a long time. It was added to Firefox in 3.6. Here's the spec. "loaded" is for older Safari browsers.

If you want to know when the page has been loaded and parsed, but all subresources have not yet been loaded (which is more akin to DOMContentLoaded), you can add the "interactive" value:

if (document.readyState === "complete" 
     || document.readyState === "loaded" 
     || document.readyState === "interactive") {
     // document has at least been parsed
}

Beyond this, if you really just want to know when DOMContentLoaded has fired, then you'll have to install an event handler for that (before it fires) and set a flag when it fires.

This MDN documentation is also a really good read about understanding more about the DOM states.