How to execute a function when page has fully loaded?

For completeness sake, you might also want to bind it to DOMContentLoaded, which is now widely supported

document.addEventListener("DOMContentLoaded", function(event){
  // your code here
});

More info: https://developer.mozilla.org/en-US/docs/Web/Events/DOMContentLoaded

Usually you can use window.onload, but you may notice that recent browsers don't fire window.onload when you use the back/forward history buttons.

Some people suggest weird contortions to work around this problem, but really if you just make a window.onunload handler (even one that doesn't do anything), this caching behavior will be disabled in all browsers. The MDC documents this "feature" pretty well, but for some reason there are still people using setInterval and other weird hacks.

Some versions of Opera have a bug that can be worked around by adding the following somewhere in your page:

<script>history.navigationMode = 'compatible';</script>

If you're just trying to get a javascript function called once per-view (and not necessarily after the DOM is finished loading), you can do something like this:

<img src="javascript:location.href='javascript:yourFunction();';">

For example, I use this trick to preload a very large file into the cache on a loading screen:

<img src="bigfile"
onload="this.location.href='javascript:location.href=\'javascript:doredir();\';';doredir();">

That's called load. It came waaaaay before DOM ready was around, and DOM ready was actually created for the exact reason that load waited on images.

window.addEventListener('load', function () {
  alert("It's loaded!")
})