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 (line.parent == null) return null;
    var cur = line.parent, no = indexOf(cur.lines, line);
    for (var chunk = cur.parent; chunk; cur = chunk, chunk = chunk.parent) {
      for (var i = 0;; ++i) {
        if (chunk.children[i] == cur) break;
        no += chunk.children[i].chunkSize();
      }
    }
    return no + cur.first;
  }
  function lineAtHeight(chunk, h) {
    var n = chunk.first;
    outer: do {
      for (var i = 0, e = chunk.children.length; i < e; ++i) {
        var child = chunk.children[i], ch = child.height;
        if (h < ch) { chunk = child; continue outer; }
        h -= ch;
        n += child.chunkSize();
      }
      return n;
    } while (!chunk.lines);
    for (var i = 0, e = chunk.lines.length; i < e; ++i) {
      var line = chunk.lines[i], lh = line.height;
      if (h < lh) break;
      h -= lh;
    }
    return n + i;
  }
  function heightAtLine(cm, lineObj) {