How to check if Font Awesome is loaded in web page with javascript?

Question

I need to check if a web page has Font Awesome in it. If not I'm going to load it with javascript. Kinda like how the facebook sdk checks to see if there is a script element containing the id "facebook-jssdk", if so it just returns (does nothing), if not it loads it. I need to do that for Font Awesome.

Answer 1

I think this is the best way to check for font-awesome, but I'm not sure if it's slower then just loading it again even if it is there.

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

window.onload = function () {
  var span = document.createElement('span');

  span.className = 'fa';
  span.style.display = 'none';
  document.body.insertBefore(span, document.body.firstChild);

  if ((css(span, 'font-family')) !== 'FontAwesome') {
    // add a local fallback
  }
  document.body.removeChild(span);
};

Answer 2

One, not sure-fire way, would be to check for the existence of the Css file. The function below would find many variations, such as ones served from a cdn, or have a "-min" suffix in the file name. There are unlikely instances this will falsely return true (if for instance somebody created an additional css file called "font-awesome-extensions.css"). A more likely problem with this approach is if a font-awesome is bundled in another file then this wouldn't find the file and falsely return false.

function findCss(fileName) {
  var finderRe = new RegExp(fileName + '.*?\.css', "i");
  var linkElems = document.getElementsByTagName("link");
  for (var i = 0, il = linkElems.length; i < il; i++) {
    if (linkElems[i].href && finderRe.test(linkElems[i].href)) {
        return true;
    }
  }
  return false;
}

console.log(findCss("font-awesome"));

Answer 3

Here's a way, but ask yourself why you're doing this? source.

/**
 * Checks if a font is available to be used on a web page.
 *
 * @param {String} fontName The name of the font to check
 * @return {Boolean}
 * @license MIT
 * @copyright Sam Clarke 2013
 * @author Sam Clarke <sam@samclarke.com>
 */
(function (document) {
    var calculateWidth, monoWidth, serifWidth, sansWidth, width;
    var body          = document.body;
    var container     = document.createElement('div');
    var containerCss  = [
        'position:absolute',
        'width:auto',
        'font-size:128px',
        'left:-99999px'
    ];

    // Create a span element to contain the test text.
    // Use innerHTML instead of createElement as it's smaller
    container.innerHTML = '<span style="' + containerCss.join(' !important;') + '">' +
        Array(100).join('wi') +
    '</span>';
    container = container.firstChild;

    calculateWidth = function (fontFamily) {
        container.style.fontFamily = fontFamily;

        body.appendChild(container);
        width = container.clientWidth;
        body.removeChild(container);

        return width;
    };

    // Pre calculate the widths of monospace, serif & sans-serif
    // to improve performance.
    monoWidth  = calculateWidth('monospace');
    serifWidth = calculateWidth('serif');
    sansWidth  = calculateWidth('sans-serif');

    window.isFontAvailable = function (fontName) {
        return monoWidth !== calculateWidth(fontName + ',monospace') ||
            sansWidth !== calculateWidth(fontName + ',sans-serif') ||
            serifWidth !== calculateWidth(fontName + ',serif');
    };
})(document);

Answer 4

You could do like this with jquery

var url = "https://maxcdn.bootstrapcdn.com/font-awesome/4.6.3/css/font-awesome.min.css";

  check if the css is loaded
  if (!$("link[href=url]").length)
    //append the link to the head tag if not loaded
    $('<link href=url rel="stylesheet">').appendTo("head")