How to know when font-face has been applied

问题:

I am currently building a corporate website for a customer that uses custom fonts extensively.

On jQuerys DOM-ready I am doing placement calculations to figure out where some pop-up menus with dynamic width and height should be placed based on their dynamic contents.

These calculations fail, since DOM-ready is fired before font-face is applied, and thus widths and heights are incorrect.

Right now (for the prototype) i am doing the calculations 500ms after DOM-ready to alleviate this problem, but this can't go into production for obvious reasons.

The problem has been observed in latest Firefox and chrome. IE 8 doesn't seem to have the problem, but then DOM-ready fires fairly late, so the delay is kind of built in I guess :)

Waiting for the load event is not an option, so my question to you is this:

Is there a reliable cross-browser way to detect when font-face has been applied?

回答1:

I found a solution after wondering why IE doesn't suffer from this problem.

Firefox and Chrome/Safari triggers the DOMContentLoaded event before font-face is applied, thus causing the problem.

The solution is to not listen for DOMContentLoaded but instead go oldschool and listen to onreadystatechange and wait until the document.readyState === 'complete' which is always triggered after font-face is applied (as far as I can tell by my tests) - which is of course what always happens in IE since it doesn't support DOMContentLoaded.

So basically you can roll-your-own event in jQuery called fontfaceapplied - maybe it should be built in ;)

document.onreadystatechange = function() {
    if (document.readyState === 'complete') 
        $(document).trigger('fontfaceapplied');
};

Funny fact: Opera does it right and waits to trigger DOMContentLoaded until font-face is applied.

回答2:

Setting the function to trigger after a timeout of 200ms solves this issue when using Google Fonts.

There's a noticeable jump, but there usually is for equal heights stuff, for the purists this might not be perfect but it works cross browser.