Check Value is a Number using isNaN() in React Native

Check for NaN

This is an example to Check Value is a Number using isNaN() in React Native. The function isNaN() is used to check the value of any variable or state is a number or not. In this example we will check input is a number or not.

To Check Value is a Number or Not

isNaN(Pass the Value to check); //It will return true if not a number else false

It can be used in if condition, as it will return the true or false condition to identify the value, is a number or not. So let’s get started.

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 command line interface to make our React Native App.

If you have previously installed a global react-native-cli package, please remove it as it may cause unexpected issues:

npm uninstall -g react-native-cli @react-native-community/cli

Run the following commands to create a new React Native project

npx react-native init ProjectName

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

npx react-native init ProjectName --version X.XX.X

Note If the above command is failing, you may have old version of react-native or react-native-cli installed globally on your pc. Try uninstalling the cli and run the cli using npx.

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

Code

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

App.js

//Check Value is a Number using isNaN() in React Native
//https://aboutreact.com/react-native-isnan-to-check-value-is-a-number-or-not/

//import React in our code
import React, {useState} from 'react';

//import all the components we are going to use
import {SafeAreaView, StyleSheet, View, Button, TextInput} from 'react-native';

const App = () => {
  const [inputValue, setInputValue] = useState('');

  const checkValueIsNumberOrNot = () => {
    //Handler called on button click
    if (isNaN(inputValue)) {
      //if input is not a number then here
      alert('It is not a Number');
    } else {
      //if input is number then here
      alert('It is a Number');
    }
  };

  return (
    <SafeAreaView style={{flex: 1}}>
      <View style={styles.container}>
        <TextInput
          placeholder="Enter text"
          onChangeText={(inputValue) => setInputValue(inputValue)}
          style={styles.textInputStyle}
        />
        <Button
          title=" Check Value Is Number Or Not "
          onPress={checkValueIsNumberOrNot}
          color="#606070"
        />
      </View>
    </SafeAreaView>
  );
};

const styles = StyleSheet.create({
  container: {
    flex: 1,
    alignItems: 'center',
    marginTop: 60,
  },
  textInputStyle: {
    textAlign: 'center',
    height: 50,
    width: '70%',
    marginBottom: 10,
  },
});

export default App;

To Run the React Native App

Open the terminal again and jump into your project using.

cd ProjectName

1. Start Metro Bundler

First, you will need to start Metro, the JavaScript bundler that ships with React Native. To start Metro bundler run following command

npx react-native start

Once you start Metro Bundler it will run forever on your terminal until you close it. Let Metro Bundler run in its own terminal. Open a new terminal and run the application.

2. Start React Native Application

To run the project on an Android Virtual Device or on real debugging device

npx react-native run-android

or on the iOS Simulator by running (macOS only)

npx react-native run-ios

Output Screenshots

This is how you can Check Value is a Number using isNaN() in React Native. 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. 🙂