React Native Global Scope Variables | Initialize once use Everywhere

Global Scope Variables

We all know either we are developing any web or any mobile app, We always need Global Scope Variables. If you are not familiar with the global variable just think about the variables which can be accessed from any screen/activity after first initialization.

They can be used on any screen as local variables but the difference is their scope is global. In React Native we can make any variable Global Scope Variables by just putting global as prefix.

Example of Global Scope Variables

If we have myvar which is a local variable and accessible only from the same class. and if we have global.myvar then it becomes global and can be accessed from any class of the application.

Here is an example to understand it. We have a global.MyVar variable initialized in the first screen which can be accessed from First Screen as well as from the Second Screen.

To Make a React Native App

Getting started with React Native will help you to know more about the way you can make a React Native project. We are going to use react-native init to make our React Native App. Assuming that you have node installed, you can use npm to install the react-native-cli command line utility. Open the terminal and go to the workspace and run

npm install -g react-native-cli

Run the following commands to create a new React Native project

react-native init ProjectName

If you want to start a new project with a specific React Native version, you can use the --version argument:

react-native init ProjectName --version X.XX.X
react-native init ProjectName --version react-native@next

This will make a project structure with an index file named App.js in your project directory.

We are going to use the react-navigation library to switch our screen so you need to install the same.

Installation of Dependencies

To switch between the screens we need to add react-navigation in our application. To install the dependencies open the terminal and jump into your project

cd ProjectName

Now run the following commands to install the dependencies

npm install @react-navigation/native --save
npm install @react-navigation/stack --save
npm install react-native-reanimated react-native-gesture-handler react-native-screens react-native-safe-area-context @react-native-community/masked-view --save

These commands will copy all the dependencies into your node_module directory.

CocoaPods Installation

Please use the following command to install CocoaPods

npx pod-install ios

Project File Structure

To start with this Example you need to create a directory named pages in your project and create two files FirstPage.js and SecondPage.js

Code

Now Open App.js in any code editor and replace the code with the following code.

App.js

// Example: React Native Global Scope Variables //
// https://aboutreact.com/react-native-global-scope-variables //
import 'react-native-gesture-handler';

import * as React from 'react';
import { Button, View, Text } from 'react-native';

import { NavigationContainer } from '@react-navigation/native';
import { createStackNavigator } from '@react-navigation/stack';

import FirstPage from './pages/FirstPage';
import SecondPage from './pages/SecondPage';

const Stack = createStackNavigator();

function App() {
  return (
    <NavigationContainer>
      <Stack.Navigator initialRouteName="FirstPage">
        <Stack.Screen
          name="FirstPage"
          component={FirstPage}
          options={{
            title: 'First Page', //Set Header Title
            headerStyle: {
              backgroundColor: '#f4511e', //Set Header color
            },
            headerTintColor: '#fff', //Set Header text color
            headerTitleStyle: {
              fontWeight: 'bold', //Set Header text style
            },
          }}
        />
        <Stack.Screen
          name="SecondPage"
          component={SecondPage}
          options={{
            title: 'Second Page', //Set Header Title
            headerStyle: {
              backgroundColor: '#f4511e', //Set Header color
            },
            headerTintColor: '#fff', //Set Header text color
            headerTitleStyle: {
              fontWeight: 'bold', //Set Header text style
            },
          }}
        />
      </Stack.Navigator>
    </NavigationContainer>
  );
}

export default App;

Open pages/FirstPage.js in any code editor and the Replace the code with the following code.

FirstPage.js

// Example: React Native Global Scope Variables //
// https://aboutreact.com/react-native-global-scope-variables //
import * as React from 'react';
import { Button, View, Text, SafeAreaView } from 'react-native';

const FirstPage = ({ navigation }) => {
  global.MyVar = 'https://aboutreact.com';

  return (
    <SafeAreaView style={{ flex: 1 }}>
      <View style={{ flex: 1 , padding: 16}}>
        <View
          style={{
            flex: 1,
            alignItems: 'center',
            justifyContent: 'center',
          }}>
          <Text
            style={{
              fontSize: 25,
              textAlign: 'center',
              marginBottom: 16
            }}>
            This is the First Page of the app
          </Text>
          <Text style={{
              fontSize: 18,
              textAlign: 'center',
              marginBottom: 16,
              color: 'red'
            }}>
            Value of Global Variable is: {global.MyVar}
          </Text>
          <Button
            onPress={() => navigation.navigate('SecondPage')}
            title="Go to Second Page"
          />
        </View>
        <Text style={{ fontSize: 18, textAlign: 'center', color: 'grey' }}>
          React Native Global Scope Variables
        </Text>
        <Text
          style={{ fontSize: 16, textAlign: 'center', color: 'grey' }}>
          www.aboutreact.com
        </Text>
      </View>
    </SafeAreaView>
  );
}

export default FirstPage;

Open pages/SecondPage.js in any code editor and the Replace the code with the following code.

SecondPage.js

// Example: React Native Global Scope Variables //
// https://aboutreact.com/react-native-global-scope-variables //
import * as React from 'react';
import { Button, View, Text, SafeAreaView } from 'react-native';

const SecondPage = ({ navigation }) => {
  return (
    <SafeAreaView style={{ flex: 1 }}>
      <View style={{ flex: 1, padding: 16 }}>
        <View
          style={{
            flex: 1,
            alignItems: 'center',
            justifyContent: 'center',
          }}>
          <Text
            style={{
              fontSize: 25,
              textAlign: 'center',
              marginBottom: 16
            }}>
            This is Second Page of the App
          </Text>
          <Text style={{
            fontSize: 18,
            textAlign: 'center',
            marginBottom: 16,
            color: 'red'
          }}>
            Value of Global Variable is: {global.MyVar}
          </Text>
        </View>
        <Text style={{ fontSize: 18, textAlign: 'center', color: 'grey' }}>
          React Native Global Scope Variables
        </Text>
        <Text
          style={{ fontSize: 16, textAlign: 'center', color: 'grey' }}>
          www.aboutreact.com
        </Text>
      </View>
    </SafeAreaView>
  );
}

export default SecondPage;

To Run the React Native App

Open the terminal again and jump into your project using.
cd ProjectName
To run the project on an Android Virtual Device or on real debugging device
react-native run-android
or on the iOS Simulator by running
react-native run-ios (macOS only).

Output Screenshot

GlobalScopeVariables1   GlobalScopeVariables2

This is how you can make a Global Scope Variables. If you have any doubts or you want to share something about the topic you can comment below or contact us here. There will be more posts coming soon. Stay tuned!

Hope you liked it. 🙂


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11 thoughts on “React Native Global Scope Variables | Initialize once use Everywhere”

    • Sharing your knowledge and suggestion is a good thing but instead of reading the code can you please run the code and try to understand the code. App.js is my index file which is used for the navigation setup of my two screens and have no component to return other than the createStackNavigator. If you have any other way can you please share it with others also?
      Thanx for your comment. 🙂

      Reply
  1. Awesome thanks. I am not inclined to learn nor adopt state management software like redux or flux e.g. But I want to learn that can we change global variable as we wish or are they constant values that should not be changed.

    Reply
    • We can change the global variable from anywhere and anytime within the application. I also want to add that we can not compare the global variable with the Redux or Flux as they can be used for managing the state from a single location and global variables just stores value and do not affect the state.

      Reply

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