feat: add custom transformers

[marcosvega91]

fix #440

This PR will add support for defaultTransformers. This could be useful if you want to apply your own body transformation as for the issue.

Now the function createResponseComposition is exported from the library. Users could create there own response function like

import fetch from 'node-fetch'
import { rest, createResponseComposition } from 'msw'
import { setupServer } from 'msw/node'
import * as JSONbig from 'json-bigint'

const customReponse = createResponseComposition({
  defaultTransformers: [
    (res) => {
      if (res.body && res.headers?.get('content-type')?.endsWith('json')) {
        res.body = JSONbig.stringify(res.body)
      }
      return res
    },
  ],
})

const server = setupServer(
  rest.get('http://test.mswjs.io/me', (req, res, ctx) => {
    const me = {
      username: 'Dude',
      balance: BigInt(1597928668063727616),
    }
    return customReponse(ctx.json(me))
  }),
)

[marcosvega91]

I have added some comments

[JesusTheHun]

Works for me !

[kettanaito]

Great work on this, @marcosvega91!

I've flattened the createResponseComposition options so we don't have to deal with default + custom options merging when given partial options object. The library now publicly exposes certain response-related TypeScript definitions so it's possible to use our internal functions and have type safety.

Looks great, I'm looking forward for the CI to pass.

[timdeschryver]

I think it would be great to add this as a recipe to the docs.
Since you implemented this feature @marcosvega91 , are you planning to add this to the recipes?
If not, I can add it (if we want to add this to the docs) 🙂

[marcosvega91]

I'm really bad writing things. Also my English is not very good, so feel free to open a PR with your changes 😉. Thanks @timdeschryver :)

[kettanaito]

@marcosvega91, thank you once more for adding these changes, Marco :)
Please, know that I'm always happy to proof-read and help with the writing. You're not alone in this.

[marcosvega91]

It's always a pleasure 🙂