In order for me to extend React-Native's WebView, I had to use Category feature objective-c, that would be the simplest and most elegant way by far.

Installation

In order to use this extension, you have to do the following steps:

in your react-native project, run npm install react-native-webview-bridge
go to xcode's Project Navigator tab
right click on Libraries
select Add Files to ... option
navigate to node_modules/react-native-webview-bridge and add WebViewBridge folder
clean compile to make sure your project can compile and build.

Usage

There is a script which will be injected by this extension to the first page that you load. In order for your webpage to get access to the injected script, you have to use the following function.

function WebViewBridgeReady(cb) {
  //checks whether WebViewBirdge exists in global scope.
  if (window.WebViewBridge) {
    cb(window.WebViewBridge);
    return;
  }

  function handler() {
    //remove the handler from listener since we don't need it anymore
    document.removeEventListener('WebViewBridge', handler, false);
    //pass the WebViewBridge object to the callback
    cb(window.WebViewBridge);
  }

  //if WebViewBridge doesn't exist in global scope attach itself to document
  //event system. Once the code is being injected by extension, the handler will
  //be called.
  document.addEventListener('WebViewBridge', handler, false);
}

so now, anywhere in your script in webpage, you can call

WebViewBridgeReady(function (WebViewBridge) {
  //at this time, you should be able to use the injected code here.
});

WebViewBridge exposes 2 methods, send and onMessage;

if you want to send a message to React-Native component, call the send method.

if you want to receive message from React-Native, attach a function to onMessage.

For Example:

WebViewBridgeReady(function (WebViewBridge) {
  WebViewBridge.onMessage = function(message) {
    console.log('got a message from react-native', message);
  };

  //sending a message to react-native
  WebViewBridge.send("Hello this is me calling from web page");
});

On React-Native side, you just have to load the WebViewBridge component.

var React = require('react-native');
var WebViewBridge = require('react-native-webview-bridge');

Since WebViewBridge is extending WebView component, it behaves exactly as WebView. What it means that WebViewBridge has all the methods and props of WebView component.

So here's an example of using WebViewBridge,

var React = require('react-native');
var WebViewBridge = require('react-native-webview-bridge');

var {
  Component
} = React;

var WEBVIEW_REF = 'my_webview';

class MyAwesomeView extends Component {
  constructor(props) {
    super(props);
  }

  componentDidMount() {
    var webviewRef = this.refs[WEBVIEW_REF];

    webviewRef.onMessage(function (message) {
      console.log("This message coming from web view", message);
      webviewRef.send("Hello from react-native");
    });
  }

  render() {
    return (
      <WebViewBridge
        ref={WEBVIEW_REF}
        url="http://<my awesome project url>"
        style={{flex: 1}}
      />
    );
  }
}