How does fetcher use url as an argument if it's never declared?

[platocrat]

My GitHub issue got moved into discussion, so I thought this would be a better location for this since it relates to the swr library.

In the index.js file in this api-routes-rest example (shown below for convenience) I cannot understand why fetcher still under the useSwr() call:

fetch() alone requires a valid url, an url which is not specified in the file, so how can line 7 in pages/index.js:

const { data, error } = useSwr('/api/users', fetcher)

be returning assigning anything to data or error??

Additional context

I am new to useSwr and maybe I am misunderstanding how the hook works, but here's what I see occuring:

1. the users API endpoint is held contained under /api/users.js and may now be used inside other function components
2. useSwr() uses the fetcher function and the users API endpoint to return the json data and an error to be assigned to data and error respectively.

In this example with data made on the same origin, I assume that useSwr() just ignores the fetcher function and things still work because the data or error being returned is a result from the requests made to the pages/api/users.js endpoint, an endpoint which already has pre-made data fed in as input and returned as a response

However, with real API GET requests from a different origin, we require that the data is pulled using some data-fetching method.

Assume we use native fetch() to create the following endpoint at pages/api/realUsers.js:

const url = 'https://api.somejson'
const liveData = fetch(url).then(res => res.json())

export default async (req, res) => {
  res.json(liveData)
}

Now, how do I consume this endpoint by using the useSwr('/api/liveData', fetcher) hook?
I can no longer use the fetcher function as:

const { data, error } = useSwr('/api/realUsers', fetcher)

because I already have my liveData contained within my liveData endpoint that I created using fetch(), and again, WHERE does the fetcher function obtain it's url from if I already used the appropriate url in creating my liveData endpoint??

[sergiodxa]

SWR falla your fetcher function passing the key as argument, in your case your URL is the key so your fetcher receives the URL from there.