Understanding next in Express.js Error Handling

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Problem Overview

You've shared an example where you're attempting to validate user data before calling a database function. The goal is simple: if some required fields are missing, you want to leverage next() to redirect to your error handling middleware instead of proceeding to execute the database call. Yet, you find that next() doesn't exit the current function. Here's a snippet of your code that illustrates the issue:

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The expectation was for next() to take you out of this logic and into your defined error handler, but the database function still gets called. Let's unpack why this is happening.

Understanding next()

What Does next() Do?

Why Use return with next()

To resolve your problem, you should use a return statement along with next(). This will ensure that once you call next(), the current function will exit immediately. Here's how the corrected code would look:

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

By adding return, you effectively stop any further lines of code in the current function from executing if the condition of missing data is met.

Alternative: Using throw

Another option you have for handling errors is by using the throw statement. If you choose to throw an error, you should also ensure that you have a catch block in place to handle the error correctly. This approach is useful when you want to encapsulate the error handling logic distinctly.

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

Conclusion