FlashLight.js

import React from "react";
import PropTypes from "prop-types";
import { Text, View, StyleSheet } from "react-native";
import { Camera, Permissions } from "expo";

/* Expo does not provide a light component, but we can control the flash using the Camera component. */
class FlashLight extends React.Component {
  static propTypes = {
    isActive: PropTypes.bool.isRequired
  };

  state = {
    hasPermissions: undefined
  };

  async componentDidMount() {
    const { status } = await Permissions.askAsync(Permissions.CAMERA);
    this.setState({ hasPermissions: status === "granted" });
  }

  render() {
    const { isActive } = this.props;
    const { hasPermissions } = this.state;
    const { FlashMode, Type } = Camera.Constants;
    const flashMode = isActive ? FlashMode.torch : FlashMode.off;

    if (hasPermissions === undefined) {
      return <View />;
    } else if (!hasPermissions) {
      return <Text>Required permissions not granted</Text>;
    } else {
      return (
        <Camera style={styles.camera} flashMode={flashMode} type={Type.back} />
      );
    }
  }
}

const styles = StyleSheet.create({
  // Set the camera component to the smallest size possible (caveat: it must be visible to work)
  camera: { flex: 0, width: 1, height: 1, opacity: 0 }
});

export default FlashLight;