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.

var lineObj = getLine(doc, line);
      var lineLen = lineObj.text.length;
      var start, end;
      function coords(ch, bias) {
        return charCoords(cm, Pos(line, ch), "div", lineObj, bias);
      }
      iterateBidiSections(getOrder(lineObj), fromArg || 0, toArg == null ? lineLen : toArg, function(from, to, dir) {
        var leftPos = coords(from, "left"), rightPos, left, right;
        if (from == to) {
          rightPos = leftPos;
          left = right = leftPos.left;
        } else {
          rightPos = coords(to - 1, "right");
          if (dir == "rtl") { var tmp = leftPos; leftPos = rightPos; rightPos = tmp; }
          left = leftPos.left;
          right = rightPos.right;
        }
        if (fromArg == null && from == 0) left = pl;
        if (rightPos.top - leftPos.top > 3) { 
          add(left, leftPos.top, null, leftPos.bottom);
          left = pl;
          if (leftPos.bottom < rightPos.top) add(left, leftPos.bottom, null, rightPos.top);
        }
        if (toArg == null && to == lineLen) right = clientWidth;
        if (!start || leftPos.top < start.top || leftPos.top == start.top && leftPos.left < start.left)
          start = leftPos;