Get rendered font-family

renderedfont.js

function getRenderedFontFamily(fontFamily) {
  var canvas = document.createElement("canvas");
  var context = canvas.getContext("2d");

  let families = fontFamily.split(/\s*,\s*/);

  for each (let family in families) {
    if (family == 'inherit') {
      return family;
    }
    var text = "abcdefghijklmnopqrstuvwxyz";

    context.font = "1000px " + family + ", serif";
    let serifWidth = context.measureText(text).width;

    context.font = "1000px " + family;
    let width1 = context.measureText(text).width;

    context.font = "1000px " + family + ", sans-serif";
    let sansWidth = context.measureText(text).width;

    context.font = "1000px " + family;
    let width2 = context.measureText(text).width;

    if (serifWidth == width1 && sansWidth == width2) {
      return family;
    }
  }
  return '';
}