App.js

import React from 'react';

import { Vibration,StyleSheet, Text, View } from 'react-native';

import { BarCodeScanner, Permissions } from 'expo';

export default class App extends React.Component {

  state = {

     hasCameraPermission:null,

  }

  async componentWillMount() {

     const { status } =await Permissions.askAsync(Permissions.CAMERA);

     this.setState({hasCameraPermission:status==='granted'});

  }

  render() {

    const { hasCameraPermission } = this.state;

    if (hasCameraPermission === null) {

    return <Text>Requesting for camera permission</Text>;

    } else if (hasCameraPermission === false) {

    return <Text>No access to camera</Text>;

    } else {

        return (

            <View style={styles.container}>

              <BarCodeScanner

                  onBarCodeRead={this._handleBarCodeRead}

                  style={{ height: 250, width: 350 }}

              />

            </View>

            );

    }

  }

  _handleBarCodeRead = ( { type, data }) => {

     alert(`Bar code type : ${type} and data : ${data} `);

      Vibration.vibrate(100);

  }

}

const styles = StyleSheet.create({

  container: {

    flex: 1,

    backgroundColor: '#fff',

    alignItems: 'center',

    justifyContent: 'center',

  },

});