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.

other.history.done = copyHistoryArray(this.history.done, splitIds);
        other.history.undone = copyHistoryArray(this.history.undone, splitIds);
      }
    },
    iterLinkedDocs: function(f) {linkedDocs(this, f);},
    getMode: function() {return this.mode;},
    getEditor: function() {return this.cm;}
  });
  Doc.prototype.eachLine = Doc.prototype.iter;
  
  var dontDelegate = "iter insert remove copy getEditor".split(" ");
  for (var prop in Doc.prototype) if (Doc.prototype.hasOwnProperty(prop) && indexOf(dontDelegate, prop) < 0)
    CodeMirror.prototype[prop] = (function(method) {
      return function() {return method.apply(this.doc, arguments);};
    })(Doc.prototype[prop]);
  eventMixin(Doc);
  function linkedDocs(doc, f, sharedHistOnly) {
    function propagate(doc, skip, sharedHist) {
      if (doc.linked) for (var i = 0; i < doc.linked.length; ++i) {
        var rel = doc.linked[i];
        if (rel.doc == skip) continue;
        var shared = sharedHist && rel.sharedHist;
        if (sharedHistOnly && !shared) continue;
        f(rel.doc, shared);
        propagate(rel.doc, doc, shared);
      }
    }
    propagate(doc, null, true);
  }
  function attachDoc(cm, doc) {