[javascript] Calculating Page Load Time In JavaScript

It is hard to make a good timing, because the performance.dominteractive is miscalulated (anyway an interesting link for timing developers).

When dom is parsed it still may load and execute deferred scripts. And inline scripts waiting for css (css blocking dom) has to be loaded also until DOMContentloaded. So it is not yet parsed?

And we have readystatechange event where we can look at readyState that unfortunately is missing "dom is parsed" that happens somewhere between "loaded" and "interactive".

Everything becomes problematic when even not the Timing API gives us a time when dom stoped parsing HTML and starting The End process. This standard say the first point has to be that "interactive" fires precisely after dom parsed! Both Chrome and FF has implemented it when document has finished loading sometime after it has parsed. They seem to (mis)interpret the standars as parsing continues beyond deferred scripts executed while people misinterpret DOMContentLoaded as something hapen before defered executing and not after. Anyway...

My recommendation for you is to read about? Navigation Timing API. Or go the easy way and choose a oneliner of these, or run all three and look in your browsers console ...

  document.addEventListener('readystatechange', function() { console.log("Fiered '" + document.readyState + "' after " + performance.now() + " ms"); });

  document.addEventListener('DOMContentLoaded', function() { console.log("Fiered DOMContentLoaded after " + performance.now() + " ms"); }, false);

  window.addEventListener('load', function() { console.log("Fiered load after " + performance.now() + " ms"); }, false);

The time is in milliseconds after document started. I have verified with Navigation? Timing API.

To get seconds for exampe from the time you did var ti = performance.now() you can do parseInt(performance.now() - ti) / 1000

Instead of that kind of performance.now() subtractions the code get little shorter by User Timing API where you set marks in your code and measure between marks.

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