Use more specific JSON types in TypeScript

[sindresorhus]

Hopefully a JSON type will be included in TypeScript at some point: microsoft/TypeScript#1897 For now, we just define it manually.

[sholladay]

Seems like a good improvement. 👍

We can deal with the enforcement of no body for GETs separately. I don't really have strong feelings about doing that anyway (it's technically allowed by the spec FYI, but highly discouraged, very much an anti-pattern, and of no practical value).

[felixfbecker]

I don't think this does what you intend it to. The way this is defined, no object is considered "JSON stringifyable" unless it has an index signature. For example, this would fail:

interface Foo { foo: number }
const foo: Foo = { foo: 123 }
const json: JSONObject = foo // Error: Foo is not assignable to JSONObject because it has no index signature

I don't think there is currently a way to express this constraint correctly.

Besides, JSON.stringify() actually doesn't care if an object has methods. It will simply omit them (unlike postMessage(), which throws an error).

[sindresorhus]

This is for the response though, not for being stringifyiable, for stringification we're quite lax:

ky/index.d.ts

Line 5 in b6ed9df

export type JSONStringifyable = string | number | boolean | null | object;