Best practices to work with undici.fetch in frameworks and libraries

[SuperOleg39]

Hello!

I want to ask for help choosing between a few approaches to working with undici.

Our case: we have a high-level universal HTTP request library based on fetch, and an SSR application built on top of this library.

First, we started migrating from node-fetch to globalThis.fetch in our request library.

After that, in the application code, we added setGlobalDispatcher(new Agent()), where Agent is imported from undici via require('undici').Agent.

Then, some of our Jest tests started failing. After continuous debugging, I found that a simple isErrorLike utility returns false for undici's SocketError, and we lose some properties like error.code.

I think this is because Jest uses node:vm to run tests. The details aren't very important for this case, but it's just an example of compatibility issues between external and bundled undici versions.

So, my question is: which approach is preferable?

• In the request library, pin a specific undici version in dependencies/peerDependencies, and import fetch from undici
• Or am I missing something important, and is it better to use globalThis.fetch, relying on the Node.js

[metcoder95]

It really depends on the kind of experience you want to give.

Using global fetch can be preferred for stability (although I have doubts fetch implementation will change even a bit across undici versions).
Relying on it will help your callers be sure that they are safe using their current Node.js features and limitations, given that the release window of Node itself.

On the other hand, always keeping undici instead, will ensure you have the latest features and optimizations of the library.

Another approach that I've seen is for libraries to use native fetch and allow callers to pass by a custom fetch implementation if they want to (allowing customization).

My suggestion is to rely on undici itself and not fetch (not within undici nor Node). But I'm unaware of your limitations and overall details to make a safe guess.

If seeking for cross compatibility (use it across browser and Node) always bet for native fetch. Otherwise undici directly instead

[SuperOleg39]

It really depends on the kind of experience you want to give.

Using global fetch can be preferred for stability (although I have doubts fetch implementation will change even a bit across undici versions).
Relying on it will help your callers be sure that they are safe using their current Node.js features and limitations, given that the release window of Node itself.

On the other hand, always keeping undici instead, will ensure you have the latest features and optimizations of the library.

Another approach that I've seen is for libraries to use native fetch and allow callers to pass by a custom fetch implementation if they want to (allowing customization).

My suggestion is to rely on undici itself and not fetch (not within undici nor Node). But I'm unaware of your limitations and overall details to make a safe guess.

If seeking for cross compatibility (use it across browser and Node) always bet for native fetch. Otherwise undici directly instead

Thanks a lot for the detailed response!

Looks like that solution with undici is most suitable for our library 👍