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 (collapsed && (collapsed.from || 0) == pos) {
          buildCollapsedSpan(builder, (collapsed.to == null ? len : collapsed.to) - pos,
                             collapsed.marker, collapsed.from == null);
          if (collapsed.to == null) return collapsed.marker.find();
        }
        if (!collapsed && foundBookmarks.length) for (var j = 0; j < foundBookmarks.length; ++j)
          buildCollapsedSpan(builder, 0, foundBookmarks[j]);
      }
      if (pos >= len) break;
      var upto = Math.min(len, nextChange);
      while (true) {
        if (text) {
          var end = pos + text.length;
          if (!collapsed) {
            var tokenText = end > upto ? text.slice(0, upto - pos) : text;
            builder.addToken(builder, tokenText, style ? style + spanStyle : spanStyle,
                             spanStartStyle, pos + tokenText.length == nextChange ? spanEndStyle : "", title);
          }
          if (end >= upto) {text = text.slice(upto - pos); pos = upto; break;}
          pos = end;
          spanStartStyle = "";
        }
        text = allText.slice(at, at = styles[i++]);
        style = interpretTokenStyle(styles[i++], builder);
      }
    }
  }
  
  function updateDoc(doc, change, markedSpans, selAfter, estimateHeight) {