ReactClass-ReactElementConstructor.js

/**
 * 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 ("production" !== process.env.NODE_ENV) {
    // 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 = {props: props, originalProps: assign({}, props)};

    // To make comparing ReactElements easier for testing purposes, we make
    // the validation flag non-enumerable (where possible, which should
    // include every environment we run tests in), so the test framework
    // ignores it.
    try {
      Object.defineProperty(this._store, 'validated', {
        configurable: false,
        enumerable: false,
        writable: true
      });
    } catch (x) {
    }
    this._store.validated = false;

    // 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;
};