加载Web字体后如何通知

问题描述

Google的Web Fonts API提供了一种定义回调函数的方法，如果字体加载完毕，或者无法加载等等，是否可以使用CSS3网络字体（@ font-face）实现类似的功能？

Google's Web Fonts API offers a way to define callback functions to be executed if a font has finished loading, or couldn't be loaded etc. Is there a way to achieve something similar using CSS3 web fonts (@font-face)?

推荐答案

2015年更新

Chrome 35+和Firefox 41+实施 CSS字体加载API （，）。调用 document.fonts 获取对象，它有一些用于检测字体加载状态的有用API：

2015 Update

Chrome 35+ and Firefox 41+ implement the CSS font loading API (MDN, W3C). Call document.fonts to get a FontFaceSet object, which has a few useful APIs for detecting the load status of fonts:

• - 返回给定字体列表中的所有字体是否已加载且可用。 fontSpec 使用。例如： document.fonts.check（'bold 16px Roboto'）; // true或false


• - 返回表示字体加载和布局操作已完成。
  示例： document.fonts .ready.then（function（）{/ * ...所有字体加载... * /}）;

• check(fontSpec) - returns whether all fonts in the given font list have been loaded and are available. The fontSpec uses the CSS shorthand syntax for fonts.
  Example: document.fonts.check('bold 16px Roboto'); // true or false
• document.fonts.ready - returns a Promise indicating that font loading and layout operations are done.
  Example: document.fonts.ready.then(function () { /*... all fonts loaded...*/ });

这是一个显示这些API的代码段，另外还有 document.fonts.onloadingdone ，它提供了有关字体面的额外信息。

Here's a snippet showing these APIs, plus document.fonts.onloadingdone, which offers extra information about the font faces.

alert('Roboto loaded? ' + document.fonts.check('1em Roboto'));  // false

document.fonts.ready.then(function () {
  alert('All fonts in use by visible text have loaded.');
   alert('Roboto loaded? ' + document.fonts.check('1em Roboto'));  // true
});

document.fonts.onloadingdone = function (fontFaceSetEvent) {
   alert('onloadingdone we have ' + fontFaceSetEvent.fontfaces.length + ' font faces loaded');
};

<link href='https://fonts.googleapis.com/css?family=Roboto:400,700' rel='stylesheet' type='text/css'>
<p style="font-family: Roboto">
  We need some text using the font, for the font to be loaded.
  So far one font face was loaded.
  Let's add some <strong>strong</strong> text to trigger loading the second one,
    with weight: 700.
</p>

IE 11不支持API。如果您需要支持IE，请查看可用的polyfill或支持库：

IE 11 doesn't support the API. Look at available polyfills or support libraries if you need to support IE:

• - 由Google和Adobe开发


• - 类似于Web Font Loader的方法


• - polyfill

• Web Font Loader - developed by Google and Adobe
• FontFaceOnload - lighter, similar approach to Web Font Loader
• FontLoader - polyfill

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