Edit in JSFiddle

"use strict";
var paragraph = "We appreciate your interest.  Please enter your email in the box below, then submit the form, and you will be subscribed to our newsletter.";

var thankYou = "Thank you for registering.  We are excited to send you your first newsletter shortly."

var Subscribe = React.createClass({
  displayName: "Subscribe",
  onClick: function() {
    this.setState({
      text: thankYou,
      label: 'Thank You',
      disabled: true
    });
  },

  componentWillMount() {
    this.setState({
      text: this.props.text,
      label: this.props.label,
      disabled: this.props.disabled
    });
  },

  render: function render() {
    return React.createElement("div", null,
      React.createElement("p", null, this.state.text),
      React.createElement("input", {
        id: "email",
        disabled: this.state.disabled
      }),
      React.createElement("button", {
        onClick: this.onClick,
        disabled: this.state.disabled
      }, this.state.label));
  }
});

ReactDOM.render(React.createElement(Subscribe, {
  text: paragraph,
  disabled: false,
  label: 'Submit'
}), document.getElementById('submitEmail'));
<div id="submitEmail"></div>