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 (nl == -1) nl = string.length;
      var line = string.slice(pos, string.charAt(nl - 1) == "\r" ? nl - 1 : nl);
      var rt = line.indexOf("\r");
      if (rt != -1) {
        result.push(line.slice(0, rt));
        pos += rt + 1;
      } else {
        result.push(line);
        pos = nl + 1;
      }
    }
    return result;
  } : function(string){return string.split(/\r\n?|\n/);};
  CodeMirror.splitLines = splitLines;
  var hasSelection = window.getSelection ? function(te) {
    try { return te.selectionStart != te.selectionEnd; }
    catch(e) { return false; }
  } : function(te) {
    try {var range = te.ownerDocument.selection.createRange();}
    catch(e) {}
    if (!range || range.parentElement() != te) return false;
    return range.compareEndPoints("StartToEnd", range) != 0;
  };
  var hasCopyEvent = (function() {
    var e = elt("div");
    if ("oncopy" in e) return true;
    e.setAttribute("oncopy", "return;");
    return typeof e.oncopy == 'function';
  })();