angular tutorial: After some time without programming, I need a refresh! :-)

 

>PROBLEM

Like as everybody never forgets... What a lie!  :-)

After sometime without using a technology, you need "swap from disk to memory".

>SOLUTION

Create a revision summary.

Example here.

>ENV

Angular

node.js: Error [ERR_HTTP_HEADERS_SENT]: Cannot set headers after they are sent to the client

 

>PROBLEM

A request generates the following error:

  Error [ERR_HTTP_HEADERS_SENT]: Cannot set headers after they are sent to the client

>SOLUTION

It happens when some exception occurs before returning the request, for instance a "res.sent" statement.

Debug the application step-by-step.

To simplify, you may comment on the code from the start.

Tip: check database exceptions not treated.

Having more than one exception becomes tricky if you can't reproduce the same request.

Be sure to fix all possible exceptions.

TIPS

- Verify database possible exceptions (undefined/null values).

- If using JWT, check possible "jwt session expired" exception.

- "if conditions" and "redirections".
Some if conditions may not avoid running the code ahead from it.

- Make sure that you have guarded your arguments checking if they are possibly null or undefined.

- Unexpected type values.
 JavaScript is not a typed language, so part of the code may get something different from expected.

The above tips are just some of them. 

>ENV

Node: 16.13.1

Package Manager: npm 8.5.4

OS: win32 x64