modernizr/feature-detects/css/fontface.js

Modernizr is a JavaScript library that detects HTML5 and CSS3 features in the user’s browser.

/*!
{
  "name": "@font-face",
  "property": "fontface",
  "authors": ["Diego Perini"],
  "tags": ["css"],
  "knownBugs": [
    "False Positive: WebOS http://github.com/Modernizr/Modernizr/issues/342",
    "False Postive: WP7 http://github.com/Modernizr/Modernizr/issues/538"
  ],
  "notes": [{
    "name": "@font-face detection routine by Diego Perini",
    "href": "http://javascript.nwbox.com/CSSSupport/"
  }]
}
!*/
define(['Modernizr', 'testStyles'], function( Modernizr, testStyles ) {
  testStyles('@font-face {font-family:"font";src:url("https://")}', function( node, rule ) {
    var style = document.getElementById('smodernizr');
    var sheet = style.sheet || style.styleSheet;
    var cssText = sheet ? (sheet.cssRules && sheet.cssRules[0] ? sheet.cssRules[0].cssText : sheet.cssText || '') : '';
    var bool = /src/i.test(cssText) && cssText.indexOf(rule.split(' ')[0]) === 0;

    Modernizr.addTest('fontface', bool);
  });
});