npm install react-native-device --save

'use strict';

var React = require('react-native');
var Device = require('react-native-device');
var {
  AppRegistry
} = React;

var ExampleApp = React.createClass({
  render: function() {
    if (Device.isIpad()) {
      // return iPad layout
    } else {
      // return iPhone layout
    }
  }
});

AppRegistry.registerComponent('ExampleApp', () => ExampleApp);