react/src/core/shouldUpdateReactComponent.js

/**
 * Copyright 2013-2014, 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 shouldUpdateReactComponent
 * @typechecks static-only
 */

"use strict";

var monitorCodeUse = require('monitorCodeUse');

/**
 * Given a `prevElement` and `nextElement`, determines if the existing
 * instance should be updated as opposed to being destroyed or replaced by a new
 * instance. Both arguments are elements. This ensures that this logic can
 * operate on stateless trees without any backing instance.
 *
 * @param {?object} prevElement
 * @param {?object} nextElement
 * @return {boolean} True if the existing instance should be updated.
 * @protected
 */
function shouldUpdateReactComponent(prevElement, nextElement) {
  if (prevElement != null && nextElement != null) {
    var prevType = typeof prevElement;
    var nextType = typeof nextElement;
    if (prevType === 'string' || prevType === 'number') {
      return (nextType === 'string' || nextType === 'number');
    } else {
      if (nextType === 'object' &&
          prevElement.type === nextElement.type &&
          prevElement.key === nextElement.key) {
        var ownersMatch = prevElement._owner === nextElement._owner;
        var prevName = null;
        var nextName = null;
        var nextDisplayName = null;
        if(__DEV__) {
          if (!ownersMatch) {
            if (prevElement._owner != null &&
                prevElement._owner.getPublicInstance() != null &&
                prevElement._owner.getPublicInstance().constructor != null) {
              prevName = prevElement._owner.getPublicInstance().constructor.displayName;
            }
            if (nextElement._owner != null &&
                nextElement._owner.getPublicInstance() != null &&
                nextElement._owner.getPublicInstance().constructor != null) {
              nextName = nextElement._owner.getPublicInstance().constructor.displayName;
            }
            if(nextElement.type != null && nextElement.type.displayName != null) {
              nextDisplayName = nextElement.type.displayName;
            }
            monitorCodeUse(
              'react_should_update_owner_is_useful',
              {
                key: prevElement.key,
                prevOwner: prevName,
                nextOwner: nextName,
                nextDisplayName: nextDisplayName
              }
            );
          }
        }
        return ownersMatch;
      }
    }
  }
  return false;
}

module.exports = shouldUpdateReactComponent;