main.js

var Component = React.createClass({
	propTypes: {
		name: React.PropTypes.string.isRequired
	},
	render: function() {
		return React.DOM.span(null, "This is a span content and my name is " + this.props.name);
	}
});

var TextAreaCounter = React.createClass({
	proptyes: {
		text: React.PropTypes.string
	},
	
	getInitialState: function() {
	  return {
		text: this.props.text,
	  };
	},
	
	_textChange: function(ev) {
	  this.setState({
		text: ev.target.value
	  });
	},

	render: function() {
		return React.DOM.div(null, 
		
		  React.DOM.textarea({
			value: this.state.text,
			onChange: this._textChange
		  }),

		  React.DOM.h3(null, this.state.text.length)
		);
	}
});

ReactDOM.render(
	React.createElement( TextAreaCounter, {
		text: "Bob"
	}),
	document.getElementById("app")
);