What could be preventing my Express error handler from being invoked after running lint on my code?

Question

What could be preventing my Express error handler from being invoked after running lint on my code?

I'm currently working on an Express app that features a custom error handler. The code for the error handler is as follows:

app.use((err: Error, _req: express.Request, res: express.Response) => {
  console.log(err)

  // ...send back a well formatted JSON error
}

However, during my testing phase, I noticed that some intentional errors are not triggering the error handler. Instead, the errors seem to be bubbling up in the test runner without any interception.

This issue cropped up after I installed ESLint and rectified all linting problems, including those related to the error handler function itself.

I'm puzzled as to why the error handler is failing to execute when errors are intentionally triggered. Any insights would be greatly appreciated!

express error-handling eslint middleware

Answer 1

Answer №1

A crucial aspect of working with error handlers in Express is ensuring they have four arguments (err, req, res, next), which sets them apart from regular request handlers that typically have three arguments (req, res, next). You can find more information on this distinction here.

The issue arose when ESLint flagged unused arguments within the handler function. In this case, both req and next were not being used. To address this, I implemented a rule where unused arguments could be prefixed with an underscore to indicate their necessity, resulting in _req. However, I decided to completely eliminate next as it was redundant for a normal function, consequently altering the argument count.

To resolve this conflict, I opted to retain next but added an underscore prefix to signal its unused status.

app.use((err: Error, _req: express.Request, res: express.Response, _next: express.NextFunction) => {

Answer 2

A crucial aspect of working with error handlers in Express is ensuring they have four arguments (err, req, res, next), which sets them apart from regular request handlers that typically have three arguments (req, res, next). You can find more information on this distinction here.

The issue arose when ESLint flagged unused arguments within the handler function. In this case, both req and next were not being used. To address this, I implemented a rule where unused arguments could be prefixed with an underscore to indicate their necessity, resulting in _req. However, I decided to completely eliminate next as it was redundant for a normal function, consequently altering the argument count.

To resolve this conflict, I opted to retain next but added an underscore prefix to signal its unused status.

app.use((err: Error, _req: express.Request, res: express.Response, _next: express.NextFunction) => {

What could be preventing my Express error handler from being invoked after running lint on my code?

Answer №1

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