ReactEmptyComponent.js

/**
 * Copyright 2014-2015, Facebook, Inc.
 * All rights reserved.
 *
 * This source code is licensed under the BSD-style license found in the
 * LICENSE file in the root directory of this source tree. An additional grant
 * of patent rights can be found in the PATENTS file in the same directory.
 *
 * @providesModule ReactEmptyComponent
 */

'use strict';

var ReactElement = require('ReactElement');
var ReactInstanceMap = require('ReactInstanceMap');

var invariant = require('invariant');

var component;
// This registry keeps track of the React IDs of the components that rendered to
// `null` (in reality a placeholder such as `noscript`)
var nullComponentIDsRegistry = {};

var ReactEmptyComponentInjection = {
  injectEmptyComponent: function(emptyComponent) {
    component = ReactElement.createFactory(emptyComponent);
  }
};

var ReactEmptyComponentType = function() {};
ReactEmptyComponentType.prototype.componentDidMount = function() {
  var internalInstance = ReactInstanceMap.get(this);
  // TODO: Make sure we run these methods in the correct order, we shouldn't
  // need this check. We're going to assume if we're here it means we ran
  // componentWillUnmount already so there is no internal instance (it gets
  // removed as part of the unmounting process).
  if (!internalInstance) {
    return;
  }
  registerNullComponentID(internalInstance._rootNodeID);
};
ReactEmptyComponentType.prototype.componentWillUnmount = function() {
  var internalInstance = ReactInstanceMap.get(this);
  // TODO: Get rid of this check. See TODO in componentDidMount.
  if (!internalInstance) {
    return;
  }
  deregisterNullComponentID(internalInstance._rootNodeID);
};
ReactEmptyComponentType.prototype.render = function() {
  invariant(
    component,
    'Trying to return null from a render, but no null placeholder component ' +
    'was injected.'
  );
  return component();
};

var emptyElement = ReactElement.createElement(ReactEmptyComponentType);

/**
 * Mark the component as having rendered to null.
 * @param {string} id Component's `_rootNodeID`.
 */
function registerNullComponentID(id) {
  nullComponentIDsRegistry[id] = true;
}

/**
 * Unmark the component as having rendered to null: it renders to something now.
 * @param {string} id Component's `_rootNodeID`.
 */
function deregisterNullComponentID(id) {
  delete nullComponentIDsRegistry[id];
}

/**
 * @param {string} id Component's `_rootNodeID`.
 * @return {boolean} True if the component is rendered to null.
 */
function isNullComponentID(id) {
  return !!nullComponentIDsRegistry[id];
}

var ReactEmptyComponent = {
  emptyElement: emptyElement,
  injection: ReactEmptyComponentInjection,
  isNullComponentID: isNullComponentID
};

module.exports = ReactEmptyComponent;