Edit in JSFiddle

<script src="https://facebook.github.io/react/js/jsfiddle-integration.js"></script>

<div id="container">
    <!-- This element's contents will be replaced with your component. -->
</div>

var Name = React.createClass({
    render: function() {
        return (
            <span>{this.props.children}</span>
        );
    }
});

var Hello = React.createClass({
    getInitialState: function() {
        return {
            greeting: "Hello"
        };
    },
    render: function() {
        var names = this.props.names;
        var results = names.map(function (result, idx) {
            var display = result;
            if (idx+1 !== names.length) {
                display += ", ";
            }
            return (
                <Name key={result}>{display}</Name>
            );
        });
    
        return (
            <div>
                <span>{this.state.greeting}&nbsp;</span>
                {results}
            </div>)
        ;
    }
});
 
React.render(<Hello names={["Jerome", "Louis", "Kathy", "Kim"]} />, document.getElementById('container'));