Error: Route.POST() requires callback functions but got a [object Undefined]

Resolving this Programmer Error in Node.js and Express.

There are two types of errors:

• Operational Errors
• Programmer Errors

A brief explanation of these two types of errors.

Operational Errors

Operational Errors represent runtime problems whose results are expected and should be dealt with in a proper way. Operational errors don’t mean the application itself has bugs, but developers need to handle them thoughtfully. Examples of operational errors include “out of memory,” “an invalid input for an API endpoint,” and so on.

Programmer Errors

Programmer Errors represent unexpected bugs in poorly written code. They mean the code itself has some issues to solve and was coded wrong. A good example is to try to read a property of “undefined.” To fix the issue, the code has to be changed. That is a bug a developer made, not an operational error.

Let’s talk about the error…

The Error Error: Route.POST() requires callback functions but got a [object Undefined] is a Programmer Error. This error could occur only due to some carelessness during writing the code. I have encountered this same error while coding a nodejs application. It took me hours to figure out a way to solve this error. I will mention my error at the end of this article. While solving this error I’ve found out that this error could occur in many ways. So, in this article, I will try to mention some of the cases when this error could show its face upon us.

• A misspelling between the router and controller file.

eg code:

The Controller function in the controller.js file.

This is the route handler

Here in the route handler, usersController() in the controller.js file is called, but there is no such function in the controller.js file. In the controller.js file, userController() is the function that is exported. So, this misspelling could raise the above error.

• module.exports() — Spelling

Check the spelling of module.exports() and exports.someFunction(). modules.export() or module.export() raise this error because the function is not properly exported due to the misspelled methods.

• Finally, let’s talk about my silly mistake…

In my case, I’ve encountered this error when I removed a function in my controller.js file but forgot to remove the same in my route handler file.

For eg,

router.get(‘/users’, controller.getUsers);

Here, I had removed the getUsers() method in the controller.js file but I still called it in my router file. so, this raised the above error.

So, Ensure the function called in the route handler is present in the controller file.

So, that’s all guys. Have a good day…