How to fix: Unhandled Promise Rejection

Unhandled Promise Rejections occur when a JavaScript Promise is rejected, and there is no .catch() handler or equivalent error-handling mechanism to manage the error. This can lead to unexpected behaviors, such as application crashes or unresponsive features, especially in production environments where such issues can degrade user experience.

Common Causes

• Missing .catch() blocks on promises.

• Errors thrown inside asynchronous functions without proper handling.

Example

async function fetchData() {
    const response = await fetch('/api/data');
    const data = await response.json();
    return data;
}
fetchData().then(data => {
    console.log(data);
});
// No catch block to handle potential errors

How to Fix

• Always Handle Rejections:

fetchData()
    .then(data => {
        console.log(data);
    })
    .catch(error => {
        console.error('Error fetching data:', error);
        // Implement fallback logic or user notifications
    });

• Use try...catch in Async Functions:

async function fetchData() {
    try {
        const response = await fetch('/api/data');
        if (!response.ok) {
            throw new Error('Network response was not ok');
        }
        const data = await response.json();
        return data;
    } catch (error) {
        console.error('Error fetching data:', error);
        // Implement fallback logic or user notifications
    }
}

Conclusion

Unhandled Promise Rejections can be a significant source of frustration in JavaScript development. By consistently handling these rejections, you can improve the stability and reliability of your applications.