brunoais brunoais - 3 months ago 32
Javascript Question

How to detect if DOMContentLoaded was fired

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 of defer and async.

What I want is simple:

How can I know that DOMContentLoaded was fired by the time the file is executed?

Why is this so difficult?

In IE, document.readyState show interactive before DOMContentLoaded.

I won't use browser detection in any way, it's against the policy of me and the rest of the participants.

What's the correct alternative?

Edit:

Seems like I wasn't clear enough. I'm not interested to know if the load event has already occurred!!! I already knew how to solve that problem! I want to know how to solve with DOMContentLoaded!!!

Answer

I would think you could use:

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 parsed, but all subresources have not yet been loaded, 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.