ReactJS findDOMNode and getDOMNode are not functions

I'm building a web-app with ReactJS and Flux and I'm trying to get the node of my current div using the method findDOMNode and I get the next error:

Uncaught TypeError: React.findDOMNode is not a function

So, I tried to use getDOMNode and I get the very same error:

Uncaught TypeError: React.getDOMNode is not a function

I'm using npm to build the JS, the code where I use these methods:

var React = require('react');
var stores = require('../stores');
var MessagesUserContainer = require('./messageusercontainer');
var ChatStore = stores.ChatStore;
var owner = stores.getOwner();

var MessagesList = React.createClass({

    getInitialState: function(){
        return {'muc': []};
    },
    componentDidUpdate: function(){
        var node = React.findDOMNode(this); //Error here
        node.scrollTop = node.scrollHeight;
    },
    render: function(){
        return (
                <div className="chatScroll">
                    {this.state.muc}
                </div>
            )
    }
});

module.exports = MessagesList;

ReactJS verion: 0.14.0

EDIT

As pointed out in the answers, the DOM library as of v0.14.0 is out of the React core, so I made a few changes to my code:

var React = require('react');
var ReactDOM = require('react-dom');
var stores = require('../stores');
var MessagesUserContainer = require('./messageusercontainer');
var ChatStore = stores.ChatStore;
var owner = stores.getOwner();

var MessagesList = React.createClass({

    getInitialState: function(){
        return {'muc': []};
    },
    componentDidUpdate: function(){
        var node = ReactDOM.findDOMNode(this);
        node.scrollTop = node.scrollHeight;
    },
    render: function(){
        return (
                <div className="chatScroll">
                    {this.state.muc}
                </div>
            )
    }
});

module.exports = MessagesList;

But I got another problem:

Uncaught Error: Invariant Violation: findDOMNode was called on an unmounted component.