title: React Native WebView onMessage and postMessage to get all web page
body: <p>I don't really clear how to implement <code>onMessage</code> and <code>postMessage</code>, can I get whole web page but only from react native side.</p>
  
  <p>I mean, I will inject this code using <code>injectedJavaScript</code></p>
  
  <pre><code>var markup = document.documentElement.innerHTML
  window.postMessage(markup)
  </code></pre>
  
  <p>and I will receive the result using <code>onMessage</code>. Is it posible cause so far I can't do that</p>