What exactly is a "frozen" processor / what is the purpose of freezing a processor?

[ben519]

New to unifiedjs. Reading the docs, I see

When processors are exposed from a module (for example, unified itself) they should not be configured directly, as that would change their behavior for all module users. Those processors are frozen and they should be called to create a new processor before they are used.

Sorry, but this isn't really clicking for me. Perhaps someone could give an example of a frozen processor versus a non frozen processor? Why might I freeze (or not freeze) a processor? Thanks!

[wooorm]

Did you click that link? https://github.com/unifiedjs/unified#processorfreeze. That's some more info and a pretty thorough example?

[ben519]

Hey thanks! I had not seen that link. Can you please tell me if my understanding is correct?

In this example, we create a processor called rehype

export const rehype = unified().use(rehypeParse).use(rehypeStringify).freeze()

We can configure it

const myNewProcessor = rehype().use(rehypeFormat)

but we cannot extend it

const myNewProcessor = rehype.use(rehypeFormat)

Why exactly does this matter? Is it that rehype().use(rehypeFormat) traverses the tree twice while rehype.use(rehypeFormat) would only traverse the tree once? Thanks!

[wooorm]

const myNewProcessor = rehype().use(rehypeFormat)

This clones (()), then configures (.use(...))

const myNewProcessor = rehype.use(rehypeFormat)

This tries to configure something that is shared with everyone. If you would be able to configure it, everyone else would also be configured.

The reason is that how you use rehype in one place, should not affect how other people, other places, use it!

Traversing trees happens somewhere else. This is unrelated to that!