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

List Every Font a User's Browser Can Display

Can JavaScript Retrieve Browser Displayable Fonts?

Yes, it is possible to obtain a list of all fonts supported by the user's browser using JavaScript. This enables the creation of a dropdown containing available fonts for user selection.

Font Detection Implementation

Refer to http://www.lalit.org/lab/javascript-css-font-detect for an efficient JavaScript solution:

Code Snippet:

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;
    };
};

Working Principle

This code exploits the unique appearance of characters across different fonts. By comparing the width and height of text rendered in a particular font against those rendered in base fonts, it determines if the target font is supported.

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