How to modify the request body using a hook

[finnbuga]

I'm looking to automatically transform from camel case to snake case all objects I'm sending in a POST request. Thought about using the beforeRequest hook. But can't figure out how to modify the body or the json object. The Request object doesn't seem to have a body property set.

[sholladay]

Request objects are immutable and while they don't have a body property, they do have various methods for reading the body.

Ky allows you to return a new request from a beforeRequest hook. So something like this should work...

import snakecaseKeys from 'snakecase-keys';
import ky from 'ky';

const api = ky.extend({
    hooks : {
        beforeRequest : [
            async (request, options) => {
                const json = await request.json();
                const snaked = snakecaseKeys(json);
                return new Request(request.url, {
                    ...options,
                    body : snaked
                });
            }
        ]
    }
});

You could further improve this hook by having it short circuit if the Content-Type header is incompatible with .json(), for example.

[finnbuga]

Thanks very much @sholladay. I've built onto your solution and came up with:

  const json = await request.json();
  const body = JSON.stringify(snakifyCase(json));
  return new Request(request, { body });

Basically I made sure that body is a string and that the new request has the same headers and all the other properties of the initial request.

[finnbuga]

Have initially tried to use

return new Request(request.url, {...request, body})

However, this doesn't work as the spread syntax doesn't spread ANY property (like request.method or request.headers). I find this very enigmatic (and frustrating). Seems like none of the Request properties are enumerable?

[sholladay]

Indeed, the properties of a request instance are not enumerable. It's frustrating, for sure. That said, I imagine they designed it like that to encourage people to use the API "correctly".

Instead of this:

new Request(request.url, {...request, body})

They want you to do this:

new Request(request, { body })