Can JavaScript Detect All Fonts a User\'s Browser Can Display?

var Detector = function() {
    // baseFonts
    var baseFonts = ['monospace', 'sans-serif', 'serif'];

    // testString
    var testString = "mmmmmmmmmmlli";

    // testSize
    var testSize = '72px';

    // helper functions
    var h = document.getElementsByTagName("body")[0];
    var s = document.createElement("span");
    s.style.fontSize = testSize;
    s.innerHTML = testString;

    // default measurements
    var defaultWidth = {};
    var defaultHeight = {};
    for (var index in baseFonts) {
        s.style.fontFamily = baseFonts[index];
        h.appendChild(s);
        defaultWidth[baseFonts[index]] = s.offsetWidth; //width for the default font
        defaultHeight[baseFonts[index]] = s.offsetHeight; //height for the defualt font
        h.removeChild(s);
    }

    this.detect = function(font) {
        var detected = false;
        for (var index in baseFonts) {
            s.style.fontFamily = font + ',' + baseFonts[index];
            h.appendChild(s);
            var matched = (s.offsetWidth != defaultWidth[baseFonts[index]] || s.offsetHeight != defaultHeight[baseFonts[index]]);
            h.removeChild(s);
            detected = detected || matched;
        }
        return detected;
    };
};