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 doc = cm.doc, x = pos.left, y;
    if (unit == "page") {
      var pageSize = Math.min(cm.display.wrapper.clientHeight, window.innerHeight || document.documentElement.clientHeight);
      y = pos.top + dir * (pageSize - (dir < 0 ? 1.5 : .5) * textHeight(cm.display));
    } else if (unit == "line") {
      y = dir > 0 ? pos.bottom + 3 : pos.top - 3;
    }
    for (;;) {
      var target = coordsChar(cm, x, y);
      if (!target.outside) break;
      if (dir < 0 ? y <= 0 : y >= doc.height) { target.hitSide = true; break; }
      y += dir * 5;
    }
    return target;
  }
  function findWordAt(line, pos) {
    var start = pos.ch, end = pos.ch;
    if (line) {
      if ((pos.xRel < 0 || end == line.length) && start) --start; else ++end;
      var startChar = line.charAt(start);
      var check = isWordChar(startChar) ? isWordChar
        : /\s/.test(startChar) ? function(ch) {return /\s/.test(ch);}
        : function(ch) {return !/\s/.test(ch) && !isWordChar(ch);};
      while (start > 0 && check(line.charAt(start - 1))) --start;
      while (end < line.length && check(line.charAt(end))) ++end;
    }
    return {from: Pos(pos.line, start), to: Pos(pos.line, end)};
  }
  function selectLine(cm, line) {