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.

else intactLines += range.to - range.from;
    }
    if (!forced && intactLines == to - from && from == display.showingFrom && to == display.showingTo) {
      updateViewOffset(cm);
      return;
    }
    intact.sort(function(a, b) {return a.from - b.from;});
    
    try {
      var focused = document.activeElement;
    } catch(e) {}
    if (intactLines < (to - from) * .7) display.lineDiv.style.display = "none";
    patchDisplay(cm, from, to, intact, positionsChangedFrom);
    display.lineDiv.style.display = "";
    if (focused && document.activeElement != focused && focused.offsetHeight) focused.focus();
    var different = from != display.showingFrom || to != display.showingTo ||
      display.lastSizeC != display.wrapper.clientHeight;
    
    
    if (different) {
      display.lastSizeC = display.wrapper.clientHeight;
      startWorker(cm, 400);
    }
    display.showingFrom = from; display.showingTo = to;
    display.gutters.style.height = "";
    updateHeightsInViewport(cm);
    updateViewOffset(cm);
    return true;
  }
  function updateHeightsInViewport(cm) {