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 (e.preventDefault) e.preventDefault();
    else e.returnValue = false;
  }
  function e_stopPropagation(e) {
    if (e.stopPropagation) e.stopPropagation();
    else e.cancelBubble = true;
  }
  function e_defaultPrevented(e) {
    return e.defaultPrevented != null ? e.defaultPrevented : e.returnValue == false;
  }
  function e_stop(e) {e_preventDefault(e); e_stopPropagation(e);}
  CodeMirror.e_stop = e_stop;
  CodeMirror.e_preventDefault = e_preventDefault;
  CodeMirror.e_stopPropagation = e_stopPropagation;
  function e_target(e) {return e.target || e.srcElement;}
  function e_button(e) {
    var b = e.which;
    if (b == null) {
      if (e.button & 1) b = 1;
      else if (e.button & 2) b = 3;
      else if (e.button & 4) b = 2;
    }
    if (mac && e.ctrlKey && b == 1) b = 3;
    return b;
  }
  
  function on(emitter, type, f) {