Right now we use codemirror's JavaScript mode on the website but there's a JSX mode now so we should start using that instead.

if (knownScrollbarWidth != null) return knownScrollbarWidth;
    var test = elt("div", null, null, "width: 50px; height: 50px; overflow-x: scroll");
    removeChildrenAndAdd(measure, test);
    if (test.offsetWidth)
      knownScrollbarWidth = test.offsetHeight - test.clientHeight;
    return knownScrollbarWidth || 0;
  }
  var zwspSupported;
  function zeroWidthElement(measure) {
    if (zwspSupported == null) {
      var test = elt("span", "\u200b");
      removeChildrenAndAdd(measure, elt("span", [test, document.createTextNode("x")]));
      if (measure.firstChild.offsetHeight != 0)
        zwspSupported = test.offsetWidth <= 1 && test.offsetHeight > 2 && !ie_lt8;
    }
    if (zwspSupported) return elt("span", "\u200b");
    else return elt("span", "\u00a0", null, "display: inline-block; width: 1px; margin-right: -1px");
  }
  
  
  var splitLines = "\n\nb".split(/\n/).length != 3 ? function(string) {
    var pos = 0, result = [], l = string.length;
    while (pos <= l) {
      var nl = string.indexOf("\n", pos);