How to know if window "load" event was fired already

I'm writing a Javascript script. This script will probably be loaded asynchronously (AMD format).

In this script, I'd like to do nothing important until the window.load event was fired. So I listen to the window "load" event.

But if the script is loaded after window.load event... how can I know window.load was already fired?

And of course I don't want to add something in any other scripts (they are all loaded async, the problem is the same) :)

Edit :

Imagine an HTML doc with no Javascript in it at all.

Than someone insert in this doc a tag, and this script tag loads my Javascript file.

This will execute my script.

How this script can know if window.load was already fired ?

No jQuery, not any script in the HTML doc before mine.

Is it possible to know ??

I found the window.document.readystate property. This property is for document "ready" event I guess, not for window "load". Is there anything similar for window "load" event ?

The easiest solution might be checking for document.readyState == 'complete', see http://www.w3schools.com/jsref/prop_doc_readystate.asp

Quick Answer

To quickly answer the question's title:

document.readyState === 'complete'

Deeper Example

Below is a nice helper if you want to call code upon a window load, while still handling the case where the window may have already loaded by the time your code runs.

function winLoad(callback) {
  if (document.readyState === 'complete') {
    callback();
  } else {
    window.addEventListener("load", callback);
  }
}

winLoad(function() {
  console.log('Window is loaded');
});

Note: code snippets on here actually don't run in the same window context so document.readyState === 'complete' actually evaluates to false when you run this. If you put the same into your console right now for this window it should evaluate as true.

See also: What is the non-jQuery equivalent of '$(document).ready()'?

Browser navigation performance loadEventEnd metric can be used to determinate if load event was triggered:

let navData = window.performance.getEntriesByType("navigation");
if (navData.length > 0 && navData[0].loadEventEnd > 0)
{
    console.log('Document is loaded');
} else {
    console.log('Document is not loaded');
}