click.js

var React = require('react');
var ReactDOM = require('react-dom');

var Append = React.createClass({
  getInitialState: function() {
    return {
      logs: []
    };
  }, 
  
  handleClick:function(clickEvent) {
    clickEvent.preventDefault();
    var logMsg = "default " + clickEvent.type  + " prevented";
    var oldLogState = this.state.logs;
    var newLogState = oldLogState.concat(logMsg);
    this.setState({logs: newLogState});
    console.log(this.state.logs);
  },
  
  render:function() {
    var logs = this.state.logs.map(function(logs, index) {
      return (
        <div key={index}> {logs} </div> 
      );
    });

    return (
      <div> 
        <a href="#" onClick={this.handleClick}>Click me</a>
        {logs} 
      </div>
    )
  }
}); 

ReactDOM.render(<Append/>, document.getElementById("main"));