React.js: Is it possible to convert a react component to HTML DOM's?

You can render a ReactElement in a detached DOM Node via React.render. Thus, the following code should work for you.

createMarker: function() {

  /** Some other lines of code */

  _this = this;

  google.maps.event.addListener(marker, 'click', function() {

    var div = document.createElement('div');
    ReactDOM.render( _this._renderInfoWindow(place), div );
    infowindow.setContent( div );
    infowindow.open(map, this);

  });

},

You could also use React's renderToString() method

_renderInfoWindow: function(place) {
  return React.renderToString(
    <div>
      <h4>{place.name}</h4>
      <p>{place.cost}</p>
      <button className="btn btn-danger btn-block" onClick={this.props.addList.bind(this, place)}>I want to go here !! </button>
    </div>
  );
}

This should work for a simple component as shown. React.renderToString() will return only the html for the component.

For newer versions of React

import ReactDOMServer from "react-dom/server";

let html = ReactDOMServer.renderToString(<div>...</div>)