How to Handle Unhandled Promise Rejections in JavaScript

Learn how to effectively manage promise rejections in JavaScript. This guide breaks down a specific problem statement and solution for handling various cases of number validation.
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How to Handle Unhandled Promise Rejections in JavaScript: A Comprehensive Guide

Handling promises effectively in JavaScript is crucial for building robust applications. However, encountering unhandled promise rejections can lead to frustrating errors in your code. In this guide, we'll explore a specific case regarding promise handling in JavaScript and provide a clear, structured solution. Let’s dive in!

Understanding the Problem

Recently, I came across a question where a developer faced the following scenario with their code:

They needed to create a function that should always return a promise.

Depending on whether the input data is a number or not, and if it is odd or even, the function should resolve or reject the promise accordingly.

Here’s the catch: the developer got an error related to unhandled promise rejections. The important details of the situation included the error message:

[[See Video to Reveal this Text or Code Snippet]]

The Original Code

Let's look at the developer's initial code to understand what went wrong:

[[See Video to Reveal this Text or Code Snippet]]

Issues Identified in the Code

Undefined Variable: The variable data is being used without being defined, which leads to a ReferenceError.

Logical Error: The conditions in the function are incorrectly checking if data is a number.

Promise Handling: There is no proper handling for the promise resolution and rejection when calling the job function.

The Solution

To resolve these issues effectively, we can refactor the code with clear logic and ensure that it handles all expected cases. Below is a concise solution that we can implement:

Refactored Code

[[See Video to Reveal this Text or Code Snippet]]

Breakdown of the Solution

Function Structure: We changed the function to accept data as an argument, ensuring it’s defined and can be checked for its type.

Condition Checks: We check if data is a number using typeof(data) === "number":

If it is a number, we use setTimeout to resolve the promise after determining if the number is odd or even.

If it is not a number, we reject the promise with the string "error".

Promise Handling: Each call to the job function is followed by .then() for a successful response and .catch() for handling any errors.

Conclusion

By structuring your promise-based code effectively and ensuring you handle all edge cases, you can avoid issues like unhandled promise rejections. Implementing these changes not only fixes the original problem but also enhances the reliability of your JavaScript applications.

Hopefully, this guide provides clarity on managing promises in your code! Happy coding!