JavaScript Async Await vs Promises Which Better Error Handling

When developers ask "javascript async await vs promises which better error handling," they often make critical mistakes that can lead to unhandled promise rejections and runtime errors. Understanding the differences between these two approaches is essential for building robust JavaScript applications.

Common Error Handling Mistakes #

Mistake 1: Mixing Async/Await with .catch() Incorrectly #

Many developers combine async/await syntax with .catch() methods, creating confusing error handling patterns:

// Wrong approach - mixing patterns
async function fetchUserData(userId) {
    const userData = await fetch(`/api/users/${userId}`)
        .catch(error => {
            console.log('Network error:', error);
            return null; // This might not be what you expect
        });
    
    // userData might be null, causing issues here
    return userData.json(); // Error: Cannot read property 'json' of null
}

The Problem: This approach can mask errors and create unexpected behavior.

Mistake 2: Forgetting Try-Catch with Async/Await #

// Wrong - no error handling
async function processData() {
    const data = await fetchData(); // Unhandled promise rejection if this fails
    const processed = await processItems(data);
    return processed;
}

Mistake 3: Not Handling Multiple Promise Rejections #

// Wrong - only catches the first error
async function fetchMultipleResources() {
    try {
        const user = await fetchUser();
        const posts = await fetchPosts(); // If this fails, user data is lost
        const comments = await fetchComments();
        return { user, posts, comments };
    } catch (error) {
        // Only the first error is caught
        return null;
    }
}

Correct Error Handling Approaches #

Async/Await with Try-Catch (Recommended for Most Cases) #

async function fetchUserData(userId) {
    try {
        const response = await fetch(`/api/users/${userId}`);
        
        if (!response.ok) {
            throw new Error(`HTTP error! status: ${response.status}`);
        }
        
        const userData = await response.json();
        return userData;
    } catch (error) {
        console.error('Failed to fetch user data:', error.message);
        throw error; // Re-throw to let caller handle
    }
}

Promise Chains with .catch() (Good for Complex Transformations) #

function fetchUserData(userId) {
    return fetch(`/api/users/${userId}`)
        .then(response => {
            if (!response.ok) {
                throw new Error(`HTTP error! status: ${response.status}`);
            }
            return response.json();
        })
        .then(userData => {
            // Transform data if needed
            return {
                ...userData,
                fullName: `${userData.firstName} ${userData.lastName}`
            };
        })
        .catch(error => {
            console.error('Failed to fetch user data:', error.message);
            throw error;
        });
}

When to Use Each Approach #

Use Async/Await When: #

• You need sequential operations
• Error handling should be localized
• Code readability is a priority
• You're working with multiple await statements

Use Promises When: #

• You need complex chaining operations
• You want to handle errors at different stages
• You're working with existing Promise-based APIs
• You need fine-grained control over error propagation

Advanced Error Handling Patterns #

Handling Multiple Independent Operations #

// Good approach for independent operations
async function fetchAllData() {
    const results = await Promise.allSettled([
        fetchUser(),
        fetchPosts(),
        fetchComments()
    ]);
    
    const errors = results
        .filter(result => result.status === 'rejected')
        .map(result => result.reason);
    
    if (errors.length > 0) {
        console.warn('Some operations failed:', errors);
    }
    
    return {
        user: results[0].status === 'fulfilled' ? results[0].value : null,
        posts: results[1].status === 'fulfilled' ? results[1].value : [],
        comments: results[2].status === 'fulfilled' ? results[2].value : []
    };
}

Creating Custom Error Types #

class APIError extends Error {
    constructor(message, status, endpoint) {
        super(message);
        this.name = 'APIError';
        this.status = status;
        this.endpoint = endpoint;
    }
}

async function fetchWithErrorHandling(url) {
    try {
        const response = await fetch(url);
        
        if (!response.ok) {
            throw new APIError(
                `Request failed: ${response.statusText}`,
                response.status,
                url
            );
        }
        
        return await response.json();
    } catch (error) {
        if (error instanceof APIError) {
            console.error(`API Error at ${error.endpoint}:`, error.message);
        } else {
            console.error('Network error:', error.message);
        }
        throw error;
    }
}

Performance Considerations #

Async/Await generally has slightly better performance for sequential operations because it doesn't create additional Promise objects for chaining.

Promises can be more efficient for complex transformation chains where intermediate values need processing.

Summary #

JavaScript async await vs promises which better error handling depends on your specific use case:

• Async/Await: Better for sequential operations with localized error handling
• Promises: Better for complex chains with staged error handling
• Both: Should always include proper error handling to prevent unhandled promise rejections

The key is consistent error handling patterns and avoiding the common mistakes of mixing approaches or forgetting error handling entirely.

Related Articles #

• Common JavaScript Async/Await Errors
• JavaScript Promise Error Handling Utilities
• How to Fix Undefined Function Errors with Callbacks