CustomWebView.js

import React, { Component, PropTypes } from 'react';
import { WebView, requireNativeComponent, NativeModules } from 'react-native';
const { CustomWebViewManager } = NativeModules; 

export default class CustomWebView extends Component {
  static propTypes = {
    ...WebView.propTypes,
    finalUrl: PropTypes.string,
    onNavigationCompleted: PropTypes.func,
  };

  static defaultProps = {
    finalUrl: 'about:blank',
  };

  _onNavigationCompleted = (event) => {
    const { onNavigationCompleted } = this.props;
    onNavigationCompleted && onNavigationCompleted(event);
  }

  render() {
    return (
      <WebView
        {...this.props}
        nativeConfig={{
          component: RCTCustomWebView,
          props: {
            finalUrl: this.props.finalUrl,
            onNavigationCompleted: this._onNavigationCompleted,
          },
          viewManager: CustomWebViewManager
        }}
      />
    );
  }
}

const RCTCustomWebView = requireNativeComponent(
  'RCTCustomWebView',
  CustomWebView,
  WebView.extraNativeComponentConfig
);