How to Fix the Cannot read properties of undefined (reading '_id') Error When Creating a User

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Understanding the Cannot read properties of undefined (reading '_id') Error

The Problem

In your signup function, everything seems to run smoothly at first. The user is created just fine; however, the response object triggers an error. When attempting to access a property from what you expect to be a user object, the response shows the following error message:

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

After logging the user variable, you find that it is returning undefined. This is particularly confusing since the signup method itself appears to create an object with all required user data.

The Root Cause

The primary issue stems from the fact that the signup method does not actually return the user object upon successful creation. When you call the signup function with:

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

you are attempting to assign the return value of the signup function to the user variable. However, since the function does not have a return statement, it returns undefined by default. Consequently, when you try to access user._id, you encounter the error because you're trying to read a property of undefined.

Solution: Returning the Created User Object

To fix this issue, a return statement must be added to the signup function. Here's how to implement this change effectively:

Step 1: Modify the signup Function

In the signup function in your user schema, ensure to return the user object after creating it. Modify the function as follows:

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Step 2: Test the signupUser Function

After making this adjustment, you'll be able to call the signup function and receive the user object in signupUser without encountering the undefined error.

Here's how the calling function should look post-modification:

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Conclusion

Encountering the Cannot read properties of undefined (reading '_id') error can be frustrating, especially when it hinders progress in your application development. In this guide, we've clarified the origins of the error—specifically, the absence of a return statement in the signup function. By implementing a simple return of the created user object, you can successfully resolve this issue and move forward with your web app development.

Follow these steps, and your signup functionality should work seamlessly, allowing for successful user creation and token generation!