javascriptreact-native

Unable to handle case of null variable in javascript/react native


I am trying to do something very simple in my react native log in screen. I first try and get the userId of a user and if it's not set I want to redirect to the user's login page. When the userId is not set I console out and get a null value for it. But when I create a if statement to check if the userId === null it doesn't work. Any ideas on what I am doing wrong?

const userId = await AsyncStorage.getItem('userId');
console.warn(userId);
console.warn("When userId is not set I get a value of null");
if (userId === null) {
    console.warn("However this check for null is not working");
    navigation.navigate("UserLoginWeb");
}

Solution

  • This is a common issue with AsyncStorage in React Native. The potential issues here could be:

    The code below is a proper way to handle this:

    import React, { useEffect } from 'react';
    import AsyncStorage from '@react-native-async-storage/async-storage';
    
    const CheckUserAuth = ({ navigation }) => {
      useEffect(() => {
        const checkUserId = async () => {
          try {
            const userId = await AsyncStorage.getItem('userId');
            console.warn('userId value:', userId);
            
            // Correct way to check for null/undefined
            if (userId == null || userId === 'null') {
              console.warn('User is not logged in');
              navigation.navigate('UserLoginWeb');
            } else {
              console.warn('User is logged in with ID:', userId);
            }
          } catch (error) {
            console.error('Error reading userId from AsyncStorage:', error);
            navigation.navigate('UserLoginWeb');
          }
        };
    
        checkUserId();
      }, [navigation]);
    
      return null; // Or your loading component
    };
    
    export default CheckUserAuth;

    The above code uses proper error handling, handles both null and "null" cases, and wrapped in useEffect to properly handle the async operation. It also includes proper TypeScript/Flow-friendly type checking.

    Make sure you're awaiting the check in a proper async context. If the code is directly in your component body rather than in a useEffect or async function, it won't work correctly. I hope this helps.