ReactElement.js

/**
 * Copyright 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 ReactElement
 */

"use strict";

var ReactContext = require('ReactContext');
var ReactCurrentOwner = require('ReactCurrentOwner');

var warning = require('warning');

var RESERVED_PROPS = {
  key: true,
  ref: true
};

/**
 * Warn for mutations.
 *
 * @internal
 * @param {object} object
 * @param {string} key
 */
function defineWarningProperty(object, key) {
  Object.defineProperty(object, key, {

    configurable: false,
    enumerable: true,

    get: function() {
      if (!this._store) {
        return null;
      }
      return this._store[key];
    },

    set: function(value) {
      warning(
        false,
        'Don\'t set the ' + key + ' property of the component. ' +
        'Mutate the existing props object instead.'
      );
      this._store[key] = value;
    }

  });
}

/**
 * This is updated to true if the membrane is successfully created.
 */
var useMutationMembrane = false;

/**
 * Warn for mutations.
 *
 * @internal
 * @param {object} element
 */
function defineMutationMembrane(prototype) {
  try {
    var pseudoFrozenProperties = {
      props: true
    };
    for (var key in pseudoFrozenProperties) {
      defineWarningProperty(prototype, key);
    }
    useMutationMembrane = true;
  } catch (x) {
    // IE will fail on defineProperty
  }
}

/**
 * Base constructor for all React elements. This is only used to make this
 * work with a dynamic instanceof check. Nothing should live on this prototype.
 *
 * @param {*} type
 * @param {string|object} ref
 * @param {*} key
 * @param {*} props
 * @internal
 */
var ReactElement = function(type, key, ref, owner, context, props) {
  // Built-in properties that belong on the element
  this.type = type;
  this.key = key;
  this.ref = ref;

  // Record the component responsible for creating this element.
  this._owner = owner;

  // TODO: Deprecate withContext, and then the context becomes accessible
  // through the owner.
  this._context = context;

  if (__DEV__) {
    // The validation flag and props are currently mutative. We put them on
    // an external backing store so that we can freeze the whole object.
    // This can be replaced with a WeakMap once they are implemented in
    // commonly used development environments.
    this._store = { validated: false, props: props };

    // We're not allowed to set props directly on the object so we early
    // return and rely on the prototype membrane to forward to the backing
    // store.
    if (useMutationMembrane) {
      Object.freeze(this);
      return;
    }
  }

  this.props = props;
};

// We intentionally don't expose the function on the constructor property.
// ReactElement should be indistinguishable from a plain object.
ReactElement.prototype = {
  _isReactElement: true
};

if (__DEV__) {
  defineMutationMembrane(ReactElement.prototype);
}

ReactElement.createElement = function(type, config, children) {
  var propName;

  // Reserved names are extracted
  var props = {};

  var key = null;
  var ref = null;

  if (config != null) {
    ref = config.ref === undefined ? null : config.ref;
    if (__DEV__) {
      warning(
        config.key !== null,
        'createElement(...): Encountered component with a `key` of null. In ' +
        'a future version, this will be treated as equivalent to the string ' +
        '\'null\'; instead, provide an explicit key or use undefined.'
      );
    }
    // TODO: Change this back to `config.key === undefined`
    key = config.key == null ? null : '' + config.key;
    // Remaining properties are added to a new props object
    for (propName in config) {
      if (config.hasOwnProperty(propName) &&
          !RESERVED_PROPS.hasOwnProperty(propName)) {
        props[propName] = config[propName];
      }
    }
  }

  // Children can be more than one argument, and those are transferred onto
  // the newly allocated props object.
  var childrenLength = arguments.length - 2;
  if (childrenLength === 1) {
    props.children = children;
  } else if (childrenLength > 1) {
    var childArray = Array(childrenLength);
    for (var i = 0; i < childrenLength; i++) {
      childArray[i] = arguments[i + 2];
    }
    props.children = childArray;
  }

  // Resolve default props
  if (type && type.defaultProps) {
    var defaultProps = type.defaultProps;
    for (propName in defaultProps) {
      if (typeof props[propName] === 'undefined') {
        props[propName] = defaultProps[propName];
      }
    }
  }

  return new ReactElement(
    type,
    key,
    ref,
    ReactCurrentOwner.current,
    ReactContext.current,
    props
  );
};

ReactElement.createFactory = function(type) {
  var factory = ReactElement.createElement.bind(null, type);
  // Expose the type on the factory and the prototype so that it can be
  // easily accessed on elements. E.g. <Foo />.type === Foo.type.
  // This should not be named `constructor` since this may not be the function
  // that created the element, and it may not even be a constructor.
  factory.type = type;
  return factory;
};

ReactElement.cloneAndReplaceProps = function(oldElement, newProps) {
  var newElement = new ReactElement(
    oldElement.type,
    oldElement.key,
    oldElement.ref,
    oldElement._owner,
    oldElement._context,
    newProps
  );

  if (__DEV__) {
    // If the key on the original is valid, then the clone is valid
    newElement._store.validated = oldElement._store.validated;
  }
  return newElement;
};

/**
 * @param {?object} object
 * @return {boolean} True if `object` is a valid component.
 * @final
 */
ReactElement.isValidElement = function(object) {
  // ReactTestUtils is often used outside of beforeEach where as React is
  // within it. This leads to two different instances of React on the same
  // page. To identify a element from a different React instance we use
  // a flag instead of an instanceof check.
  var isElement = !!(object && object._isReactElement);
  // if (isElement && !(object instanceof ReactElement)) {
  // This is an indicator that you're using multiple versions of React at the
  // same time. This will screw with ownership and stuff. Fix it, please.
  // TODO: We could possibly warn here.
  // }
  return isElement;
};

module.exports = ReactElement;