code: function(
        prevComponent,
        nextElement,
        container,
        callback) {
      if ("production" !== "development") {
        ReactElementValidator.checkAndWarnForMutatedProps(nextElement);
      }
  
      ReactMount.scrollMonitor(container, function() {
        ReactUpdateQueue.enqueueElementInternal(prevComponent, nextElement);
        if (callback) {
          ReactUpdateQueue.enqueueCallbackInternal(prevComponent, callback);
        }
      });
  
      if ("production" !== "development") {
        // Record the root element in case it later gets transplanted.
        rootElementsByReactRootID[getReactRootID(container)] =
          getReactRootElementInContainer(container);
      }
  
      return prevComponent;
    }
docs: Take a component that's already mounted into the DOM and replace its props
  @param {ReactComponent} prevComponent component instance already in the DOM
  @param {ReactElement} nextElement component instance to render
  @param {DOMElement} container container to render into
  @param {?function} callback function triggered on completion