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 off = cm.display.viewOffset = heightAtLine(cm, getLine(cm.doc, cm.display.showingFrom));
    
    cm.display.mover.style.top = off + "px";
  }
  function computeIntact(intact, changes) {
    for (var i = 0, l = changes.length || 0; i < l; ++i) {
      var change = changes[i], intact2 = [], diff = change.diff || 0;
      for (var j = 0, l2 = intact.length; j < l2; ++j) {
        var range = intact[j];
        if (change.to <= range.from && change.diff) {
          intact2.push({from: range.from + diff, to: range.to + diff});
        } else if (change.to <= range.from || change.from >= range.to) {
          intact2.push(range);
        } else {
          if (change.from > range.from)
            intact2.push({from: range.from, to: change.from});
          if (change.to < range.to)
            intact2.push({from: change.to + diff, to: range.to + diff});
        }
      }
      intact = intact2;
    }
    return intact;
  }
  function getDimensions(cm) {