function createClass(spec) {
	    // To keep our warnings more understandable, we'll use a little hack here to
	    // ensure that Constructor.name !== 'Constructor'. This makes sure we don't
	    // unnecessarily identify a class without displayName as 'Constructor'.
	    var Constructor = identity(function(props, context, updater) {
	      // This constructor gets overridden by mocks. The argument is used
	      // by mocks to assert on what gets mounted.

	      if (false) {
	        warning(
	          this instanceof Constructor,
	          'Something is calling a React component directly. Use a factory or ' +
	            'JSX instead. See: https://fb.me/react-legacyfactory'
	        );
	      }

	      // Wire up auto-binding
	      if (this.__reactAutoBindPairs.length) {
	        bindAutoBindMethods(this);
	      }

	      this.props = props;
	      this.context = context;
	      this.refs = emptyObject;
	      this.updater = updater || ReactNoopUpdateQueue;

	      this.state = null;

	      // ReactClasses doesn't have constructors. Instead, they use the
	      // getInitialState and componentWillMount methods for initialization.

	      var initialState = this.getInitialState ? this.getInitialState() : null;
	      if (false) {
	        // We allow auto-mocks to proceed as if they're returning null.
	        if (
	          initialState === undefined &&
	          this.getInitialState._isMockFunction
	        ) {
	          // This is probably bad practice. Consider warning here and
	          // deprecating this convenience.
	          initialState = null;
	        }
	      }
	      _invariant(
	        typeof initialState === 'object' && !Array.isArray(initialState),
	        '%s.getInitialState(): must return an object or null',
	        Constructor.displayName || 'ReactCompositeComponent'
	      );

	      this.state = initialState;
	    });
	    Constructor.prototype = new ReactClassComponent();
	    Constructor.prototype.constructor = Constructor;
	    Constructor.prototype.__reactAutoBindPairs = [];

	    injectedMixins.forEach(mixSpecIntoComponent.bind(null, Constructor));

	    mixSpecIntoComponent(Constructor, IsMountedPreMixin);
	    mixSpecIntoComponent(Constructor, spec);
	    mixSpecIntoComponent(Constructor, IsMountedPostMixin);

	    // Initialize the defaultProps property after all mixins have been merged.
	    if (Constructor.getDefaultProps) {
	      Constructor.defaultProps = Constructor.getDefaultProps();
	    }

	    if (false) {
	      // This is a tag to indicate that the use of these method names is ok,
	      // since it's used with createClass. If it's not, then it's likely a
	      // mistake so we'll warn you to use the static property, property
	      // initializer or constructor respectively.
	      if (Constructor.getDefaultProps) {
	        Constructor.getDefaultProps.isReactClassApproved = {};
	      }
	      if (Constructor.prototype.getInitialState) {
	        Constructor.prototype.getInitialState.isReactClassApproved = {};
	      }
	    }

	    _invariant(
	      Constructor.prototype.render,
	      'createClass(...): Class specification must implement a `render` method.'
	    );

	    if (false) {
	      warning(
	        !Constructor.prototype.componentShouldUpdate,
	        '%s has a method called ' +
	          'componentShouldUpdate(). Did you mean shouldComponentUpdate()? ' +
	          'The name is phrased as a question because the function is ' +
	          'expected to return a value.',
	        spec.displayName || 'A component'
	      );
	      warning(
	        !Constructor.prototype.componentWillRecieveProps,
	        '%s has a method called ' +
	          'componentWillRecieveProps(). Did you mean componentWillReceiveProps()?',
	        spec.displayName || 'A component'
	      );
	    }

	    // Reduce time spent doing lookups by setting these on the prototype.
	    for (var methodName in ReactClassInterface) {
	      if (!Constructor.prototype[methodName]) {
	        Constructor.prototype[methodName] = null;
	      }
	    }

	    return Constructor;
	  }
Creates a composite component class given a class specification.
See https://facebook.github.io/react/docs/top-level-api.html#react.createclass

@param {object} spec Class specification (which must define `render`).
@return {function} Component constructor function.
@public