In RTK, I'm using a custom baseQuery to wrap axios, following the general guidance here. However, I can't seem to figure out a way to use conditional typing for the BaseQueryArg type. For example, I'd like to be able to have my baseQuery function take in the following argument object:
{
url: string
method: "GET" | "PUT" | "POST" | "DELETE"
body: any
}
But, rather than have body be any, or even a stricter union, I'd like to have it vary depend on the type of method. So, for example, if this was a simple function I would type it like so:
function myBaseQueryFunction<T extends "GET"|"POST">(args: {
url: string
method: T
body: T extends "POST" ? {someBodyData: string} : null
}){
// do the query
}
However, I can't seem to find any way to use that kind of typing for the function I pass to baseQuery and have it properly restrict the return types of of my query endpoints. Even if I don't use the BaseQueryFn utility type and, instead, manually type a function like the one above and then pass it to baseQuery, I still don't get the restriction on query's return that I want.
Is there anyway to do this kind of conditional typing of baseQuery?
Update
Per the accepted answer below, the simplest way to handle this is with a discriminated union on method, e.g.:
type BaseQueryDiscriminatedArg =
| {
url: string
method: "POST"
body: {someBodyData: string}
}
| {
url: string
method: "GET"
body?: null
}
and then your BaseQueryFn type is just BaseQueryFn<BaseQueryDiscriminatedArg>
