list every font a user's browser can display

Is there a way in javascript to obtain the names of all fonts (or font-families) that the browser can show? (I want to give the user a dropdown with a list of all available fonts, and allow the user to choose a font.) I'd prefer not to have to hardcode this list ahead of time or send it down from the server. (Intuitively, it seems like the browser should know what fonts it has and this should be exposed to javascript somehow.)

Answers:

Answer

The JavaScript version is a bit flaky. It gets fonts by iterating through known fonts and testing.

The most accurate way (albeit having to use a propriety plugin) is to use Flash. Here you can get the list of fonts without having to test for them individually using dimensions.

You are going have to decide whether to have an exact list at the expense of not working on some devices ( iDevices, browsers without Flash plugin, etc), or a partial list with better support via JavaScript only.

Answer

Yes there is! I'm so glad you asked this question because I now want to use this too.

+1 for question, and here's your answer :)

http://www.lalit.org/lab/javascript-css-font-detect

Code from http://www.lalit.org/wordpress/wp-content/uploads/2008/05/fontdetect.js?ver=0.3

/**
 * JavaScript code to detect available availability of a
 * particular font in a browser using JavaScript and CSS.
 *
 * Author : Lalit Patel
 * Website: http://www.lalit.org/lab/javascript-css-font-detect/
 * License: Apache Software License 2.0
 *          http://www.apache.org/licenses/LICENSE-2.0
 * Version: 0.15 (21 Sep 2009)
 *          Changed comparision font to default from sans-default-default,
 *          as in FF3.0 font of child element didn't fallback
 *          to parent element if the font is missing.
 * Version: 0.2 (04 Mar 2012)
 *          Comparing font against all the 3 generic font families ie,
 *          'monospace', 'sans-serif' and 'sans'. If it doesn't match all 3
 *          then that font is 100% not available in the system
 * Version: 0.3 (24 Mar 2012)
 *          Replaced sans with serif in the list of baseFonts
 */

/**
 * Usage: d = new Detector();
 *        d.detect('font name');
 */
var Detector = function() {
    // a font will be compared against all the three default fonts.
    // and if it doesn't match all 3 then that font is not available.
    var baseFonts = ['monospace', 'sans-serif', 'serif'];

    //we use m or w because these two characters take up the maximum width.
    // And we use a LLi so that the same matching fonts can get separated
    var testString = "mmmmmmmmmmlli";

    //we test using 72px font size, we may use any size. I guess larger the better.
    var testSize = '72px';

    var h = document.getElementsByTagName("body")[0];

    // create a SPAN in the document to get the width of the text we use to test
    var s = document.createElement("span");
    s.style.fontSize = testSize;
    s.innerHTML = testString;
    var defaultWidth = {};
    var defaultHeight = {};
    for (var index in baseFonts) {
        //get the default width for the three base fonts
        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);
    }

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

    this.detect = detect;
};

Summary

How does it work?

This code works on the simple principle that each character appears differently in different fonts. So different fonts will take different width and height for the same string of characters of same font-size.

Answer

In my search for this, I also found Font.js, which adds a Font object much like Image, so it's possible to check when a font is actually ready to use. Also works on installed/system fonts. Downside is IE9+ only due to needing Object.defineProperty (other browsers have it), but if you are doing modern web, this seems like an even better option. (I will, sadly, have to go with the answer above, upvoted and moving on for now. :))

Answer

I added two methods to Lalit Patel's Detector above :

  • addFont(family, stylesheetUrl, ruleString) -> detects if the font 'family' exists, if not adds a stylesheet loading the font using either stylesheetUrl if given or otherwise ruleString
  • addFontsArr(arr) -> adds an array of fonts

With this you can do:

fonts = [ 'Arial', 'Arial Black', { family: 'Lato', stylesheetUrl: 'https://fonts.googleapis.com/css?family=Lato'}, 'Leelawadee UI']
(new FontDetector()).addFontsArr(fonts);

code:

/**
 * JavaScript code to detect available availability of a
 * particular font in a browser using JavaScript and CSS.
 *
 * Author : Lalit Patel
 * Website: http://www.lalit.org/lab/javascript-css-font-detect/
 * License: Apache Software License 2.0
 *          http://www.apache.org/licenses/LICENSE-2.0
 * Version: 0.15 (21 Sep 2009)
 *          Changed comparision font to default from sans-default-default,
 *          as in FF3.0 font of child element didn't fallback
 *          to parent element if the font is missing.
 * Version: 0.2 (04 Mar 2012)
 *          Comparing font against all the 3 generic font families ie,
 *          'monospace', 'sans-serif' and 'sans'. If it doesn't match all 3
 *          then that font is 100% not available in the system
 * Version: 0.3 (24 Mar 2012)
 *          Replaced sans with serif in the list of baseFonts
 */

/**
 * Usage: d = new Detector();
 *        d.detect('font name');
 */
function FontDetector() {
    this.detect = detect;
    this.addFont = addFont;
    this.addFontsArr = addFontsArr;

    // a font will be compared against all the three default fonts.
    // and if it doesn't match all 3 then that font is not available.
    var baseFonts = ['monospace', 'sans-serif', 'serif'];

    //we use m or w because these two characters take up the maximum width.
    // And we use a LLi so that the same matching fonts can get separated
    var testString = "mmmmmmmmmmlli";

    //we test using 72px font size, we may use any size. I guess larger the better.
    var testSize = '72px';

    var h = document.getElementsByTagName("body")[0];

    // create a SPAN in the document to get the width of the text we use to test
    var s = document.createElement("span");
    s.style.fontSize = testSize;
    s.innerHTML = testString;
    var defaultWidth = {};
    var defaultHeight = {};
    for (var index in baseFonts) {
        //get the default width for the three base fonts
        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);
    }

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

    function addFont(family, stylesheetUrl, ruleString) {
        if (detect(family)) {
            //console.log('using internal font '+family);
            return true;
        }
        if (stylesheetUrl) {
            console.log('added stylesheet '+stylesheetUrl);
            var head = document.head, link = document.createElement('link');
            link.type = 'text/css';
            link.rel = 'stylesheet';
            link.href = stylesheetUrl;
            head.appendChild(link);
            return true;          
        }

        if (ruleString) {
            console.log('adding font rule:'+rule);
            var newStyle = document.createElement('style');
            newStyle.appendChild(document.createTextNode(rule));
            document.head.appendChild(newStyle);
            return true;
        }

        console.log('could not add font '+family);
    }

    function addFontsArr(arr) {
        arr.forEach(a => typeof a==='string' ? addFont(a) : addFont(a.family, a.stylesheetUrl, a.ruleString));
    }
};
Answer

Go to deviceinfo.me and click on the font detection button.

Answer

Maybe this could be done in a completely different way, using a spritesheet with known font images for a specific character and comparing that with snapshots of a canvas element on which the same character is drawn with what the browser reports as the same font. The comparison may be done with something like resemble.js.

This is slower, but should also allow us to detect when the browser is lying.

Answer

I have recently noticed that if I set the context.font value for an HTML5 canvas, to something invalid, such as "junk", the change is ignored by the canvas. I do not know if this is browser specific, but it seems to work this way on Chrome. I have also seen other posts (HTML 5 canvas font being ignored) that indicate it happens in other browsers.

One could then write a string out with the default value, which I believe is "10px sans serif" (https://developer.mozilla.org/en-US/docs/Web/API/CanvasRenderingContext2D/font), set the font to one you are testing and write the string again. If it is the same as the first drawing, then the font is not available.

Answer
<SCRIPT>
    function getFonts()
    {
        var nFontLen = dlgHelper.fonts.count;
        var rgFonts = new Array();
        for ( var i = 1; i < nFontLen + 1; i++ )
            rgFonts[i] = dlgHelper.fonts(i); 

        rgFonts.sort();
        for ( var j = 0; j < nFontLen; j++ )
            document.write( rgFonts[j] + "<BR>" );
    }
</SCRIPT>

<BODY onload="getFonts()">
<OBJECT id=dlgHelper CLASSID="clsid:3050f819-98b5-11cf-bb82-00aa00bdce0b" width="0px" height="0px">
</OBJECT>

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