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.

return intoCoordSystem(this, getLine(this.doc, line), {top: 0, left: 0}, mode || "page").top +
        (end ? lineObj.height : 0);
    },
    defaultTextHeight: function() { return textHeight(this.display); },
    defaultCharWidth: function() { return charWidth(this.display); },
    setGutterMarker: operation(null, function(line, gutterID, value) {
      return changeLine(this, line, function(line) {
        var markers = line.gutterMarkers || (line.gutterMarkers = {});
        markers[gutterID] = value;
        if (!value && isEmpty(markers)) line.gutterMarkers = null;
        return true;
      });
    }),
    clearGutter: operation(null, function(gutterID) {
      var cm = this, doc = cm.doc, i = doc.first;
      doc.iter(function(line) {
        if (line.gutterMarkers && line.gutterMarkers[gutterID]) {
          line.gutterMarkers[gutterID] = null;
          regChange(cm, i, i + 1);
          if (isEmpty(line.gutterMarkers)) line.gutterMarkers = null;
        }
        ++i;
      });
    }),
    addLineClass: operation(null, function(handle, where, cls) {
      return changeLine(this, handle, function(line) {
        var prop = where == "text" ? "textClass" : where == "background" ? "bgClass" : "wrapClass";
        if (!line[prop]) line[prop] = cls;
        else if (new RegExp("(?:^|\\s)" + cls + "(?:$|\\s)").test(line[prop])) return false;
        else line[prop] += " " + cls;