JSFiddle - React, Tailwind, and code Playground

HTML

<script src="http://fb.me/JSXTransformer-0.10.0.js"></script>
<script src="http://fb.me/react-with-addons-0.10.0.js"></script>
<script src="http://fb.me/react-js-fiddle-integration.js"></script>

CSS

div { background: #ccc; }

JavaScript 1.7

/** @jsx React.DOM */

var World = React.createClass({
    getInitialState: function() {
        return { width: 0 }
    },
    componentDidMount: function() {
        this.setState({ width: 100 })
    },
    componentDidUpdate: function() {
        console.log(this.getDOMNode().innerHTML);
    },
    render: function() {
        var width
        var children = React.Children.map(this.props.children, function(child, i) {
            var width = i*this.state.width
            console.log('Setting width: '+width);
            return React.addons.cloneWithProps(child, {style: {width: width + 'px'}})
        }, this)
        return <div>{children}</div>
    }
 })

var Hello = React.createClass({
    render: function() {
        return (
            <World>
                <div>1</div>
                <div>1</div>
            </World>
        )
    }
})

React.renderComponent(<Hello />, document.body);