How to type normal fetch() return value

type Activity = {
  activity: string
  type: string
  participants: number
  price: number
  link: string
  key: string
  accessibility: number
}

async function fetchOne(): Promise<Activity> {
  const url = "https://www.boredapi.com/api/activity"
  const res: Activity = await fetch(url).then(res => (res.json()))
  // Unsafe assignment of an `any` value.eslint@typescript-eslint/no-unsafe-assignment
  // how to fix this? 
  return res
}

I got :

> Unsafe assignment of an any value.eslint@typescript-eslint/no-unsafe-assignment

Any suggestion on how to fix this?

> Any suggestion on how to fix this?

You can't.

The return type of an operation over the wire is fundamentally, logically unknowable at compile-time. You can't statically analyze something like that. The proper return type of response.json() should really be unknown.

All you can do with dynamic data is add runtime checks to ensure that it conforms to the schema you want and move the data into type-safe constructs:

type Thing = {
  a: string
  b: number
}

async function getTheThing(): Promise<Thing> {
  const resp = await fetch('someurl');
  const data: unknown = resp.json();
  if (typeof data === 'object' && data && 'a' in data && 'b' in data && typeof data.a === 'string' && typeof data.b === 'number') {
    return {
      a: data.a,
      b: data.b
    }
  }

  throw new Error('bad data!')
}

Playground

Note the compiler accepts this without any unsafe casts. Also note the cumbersome conditional logic. You can move it into a user-defined type predicate to make it a little more ergonomical to use.