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.

while (at < end) {
          var i_end = st[i];
          if (i_end > end)
            st.splice(i, 1, end, st[i+1], i_end);
          i += 2;
          at = Math.min(end, i_end);
        }
        if (!style) return;
        if (overlay.opaque) {
          st.splice(start, i - start, end, style);
          i = start + 2;
        } else {
          for (; start < i; start += 2) {
            var cur = st[start+1];
            st[start+1] = cur ? cur + " " + style : style;
          }
        }
      });
    }
    return st;
  }
  function getLineStyles(cm, line) {
    if (!line.styles || line.styles[0] != cm.state.modeGen)
      line.styles = highlightLine(cm, line, line.stateAfter = getStateBefore(cm, lineNo(line)));
    return line.styles;
  }
  
  
  function processLine(cm, text, state, startAt) {