CODEWITHSUNDEEP
typescriptcurrying
dwjohnston
dwjohnston

Reputation: 11812

Typescript interface for a function that returns a function

I have a StoryOptions object, that one of its properties is actionFn, which when called, will return a function. (I'm making use of function currying).

This actionFn needs to accept an object of type ActionBundle, and it will return a function that accepts a Payload and returns a ReduxAction.

How do I define the StoryOptions interface in typescript?

I have tried: 

interface StoryOptions {
    baseName: string; 
    actionFn(actions: ActionBundle): ((payload: Payload): ReduxAction); 
}

But this tells me:

'ReduxAction' only refers to a type, but is being used as a value here.ts(2693)

Upvotes: 2

Views: 5361

Answers (2)

hackape
hackape

Reputation: 19957

It should be

interface StoryOptions {
  actionFn(actions: ActionBundle): (payload: Payload) => ReduxAction; 
}

Two ways you can specify a callable interface in TS.

type Callable = { (...args: any[]): any }
// or
type Callable = (...args: any[]) => any

With 1st syntax, the surrounding { } is required. That's what you missed.

Upvotes: 2

marsibarsi
marsibarsi

Reputation: 1073

You can show that it is a function this way:

interface StoryOptions {
    baseName: string; 
    actionFn(actions: ActionBundle): ((payload: Payload) => ReduxAction); 
}

Upvotes: 2

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