How to get the actual rendered font when it's not defined in CSS?

How do I get the actual font face and font size of an element when the CSS font-face and font-size properties are not defined?

For example, the JavaScript snippet

object.style.fontFamily

does not return any value. That's pretty obvious, assuming CSS hasn't applied a style to object anywhere. But, of course, a certain font is used to render the text, probably the system font or the webbrowser default font.

So can, for instance, JavaScript get that rendered font?

Answers:

Answer

I suggest this function:

function css( element, property ) {
    return window.getComputedStyle( element, null ).getPropertyValue( property );
}

Usage:

css( object, 'font-size' ) // returns '16px' for instance

Note: getComputedStyle doesn't work in IE8.

Live demo: http://jsfiddle.net/4mxzE/

Answer

There is no standard, reliable method for determining the actual font being used. The previous answers here will report the styled fontFamily style value, but that can be a list of font names and doesn't specifically identify the actual font rendered (which was the actual question posed here).

(As mentioned in some comments, there are ways to guess at the font by inspecting visual cues, but that isn’t likely to be 100% reliable.)

Answer

You can find the information about the rendered font in Chrome/Firefox Developer Tools. Try inspecting the paragraph in the following code snippet:

p { font-family: sans-serif;  }
<p>Some text and <span title="an emoji">????</span></p>


In Chrome Developer Tools (tested on 55.0.2883.75 m 64-bit) you get the following information:

Chrome Developer Tools > Element > Computed Tab


In Firefox Developer Tools (tested on 47.0.2 with about:config > devtools.fontinspector.enabled = true) you get the following information:

Firefox Developer Tools > Element > Fonts Tab

Answer

I found a way (for all browsers which support <canvas>), by checking pixel for pixel if the font rendering has changed

function renderedfont(ele) {
    var getDefaultFonts = function () {
        var iframe = document.createElement('iframe');
        var html = '<html><body>';
        var fonts;
        document.body.appendChild(iframe);
        iframe.contentWindow.document.open();
        iframe.contentWindow.document.write(html);
        var subele = iframe.contentWindow.document.createElement(ele.tagName);
        iframe.contentWindow.document.body.appendChild(subele);
        fonts = getComputedStyle(subele)['font-family'];
        document.body.removeChild(iframe);
        return fonts;
    }
    var fonts = getComputedStyle(ele)['font-family'] + ',' + getDefaultFonts();
    var fontsArray = fonts.split(',');
    var canvas = document.createElement('canvas');
    var ctx = canvas.getContext("2d");
    var testString = "[email protected]#$%^&*()ñ";
    var prevImageData;
    document.body.appendChild(canvas);
    canvas.width = 500;
    canvas.height = 300;
    fontsArray.unshift('"Font That Doesnt Exists ' + Math.random() + '"');

    for (var i = 0; i < fontsArray.length; i++) {
        var fontName = fontsArray[i].trim();
        ctx.clearRect(0, 0, canvas.width, canvas.height);
        ctx.font = '16px ' + fontName + ', monospace';
        ctx.fillText(testString, 10, 100);
        var idata = ctx.getImageData(0, 0, canvas.width, canvas.height); 
        var data = idata.data
        if (prevImageData) {
            for (var j = 0; j < data.length; j += 3) {
                if (prevImageData[j + 3] !== data[j + 3]) {
                    document.body.removeChild(canvas);
                    return fontName;
                }
            }
        }
        prevImageData = data;
    }

    document.body.removeChild(canvas);
    return 'monospace';
}

So to use you just do:

renderedfont(document.body);
// Arial

If you are using this for another dialect (e.g. japanese) you may want to change the testString variable to the most common characters in that dialect.

Answer

Being a bit late here, but having had to solve the same problem... Šime Vidas's answer is basically correct, but nowadays, you can get creative, and have your answer.

Basically, define your own font-face, which you are sure does not match any existing font. Then, add your font after each computedstyle font, and see if it's your font that get rendered. If it's not, congrats, you found the rendered font

Here is the fiddle: https://jsfiddle.net/obutjanw/

this is the code that defines the function you need:

    (function(win) {

        var style = null;
        function createClass(name,rules){
            if (typeof(rules)!="string") {
                rules = JSON.stringify(rules).trim();
            }

            if (rules.startsWith("{")&&rules.endsWith("}")) {
                rules = rules.substring(1,rules.length-1);
            }

            if (style==null) {
                style = document.createElement('style');
                style.type = 'text/css';
                var head = document.getElementsByTagName('head');
                if (head.length=0) {
                    var h = document.createElement('head');
                    document.insertBefore(h,document.body);
                    head = [h];
                }
                head[0].appendChild(style);
            }


            var rule;
            if(!(style.sheet||{}).insertRule) {
                rule = (style.styleSheet || style.sheet).addRule(name, rules);
            } else {
                style.sheet.insertRule(name+"{"+rules+"}",0);
                rule = style.sheet
            }
            return rule;
        }

        function removeNode(node) {
            if (node.remove) {
                node.remove();
            } else {
                var pn = node.parentElement;
                if (pn!=null) {
                    pn.removeChild(node);
                }
            }
        }



        createClass("@font-face", "{ font-family: 'void';  src: url(data:application/font-woff2;charset=utf-8;base64,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) format('woff2'), url(data:application/font-woff;charset=utf-8;base64,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) format('woff'); }");


        var tests = document.createElement("span");
        tests.innerHTML = "0123";
        tests.style.display = "inline-block";
        tests.style.fontFamily = "void";
        document.body.appendChild(tests);
        setTimeout(function() {
            removeNode(tests);
        },0);

        function getRenderedFontFamily(elm, computedstyle) {
            var cs = (typeof(computedstyle) == 'undefined') ? win.getComputedStyle(elm) : computedstyle;
            var fontF   = (cs.fontFamily        || elm.style['font-family'] || '').replace(/['"]*/g, '');
            var tfontF = fontF.split(",");
            var tests = document.createElement("span");
            tests.innerHTML = "0123";
            tests.style.display = "inline-block";
            tests.style.fontFamily = "void";
            elm.appendChild(tests);
            var refcs = window.getComputedStyle(tests);
            var refw = refcs.width;
            var tested = {};
            while (tfontF!=null) {
                for (var i=0;i<tfontF.length;i++) {
                    if (tested[tfontF[i]]) continue;
                    tests.style.fontFamily = tfontF[i] + ", void";
                    if (refcs.width!=refw) {
                        removeNode(tests);
                        return tfontF[i].trim();
                    }
                    tested[tfontF[i]] = true;
                }
                if (elm.parentElement) {
                    elm = elm.parentElement;
                    var cs1 = win.getComputedStyle(elm);
                    fontF   = (cs1.fontFamily       || elm.style['font-family'] || '').replace(/['"]*/g, '');
                    tfontF = fontF.split(",");
                } else {
                    tfontF = null;
                }
            }
            removeNode(tests);
        }
        win.getRenderedFontFamily =  getRenderedFontFamily;
    })(window);

Note that you really should keep the part were a node using the font is appended on load, as otherwise the browser may be late rendering the corect font on the first call to getRenderedFontFamily

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