is it posible to change the type of something based on the value of an argument passed to a function. I need this kind of type for an event emiter with callback. Example:

interface IUser {
  name: string
}

type CallBack = /* the Type for the Callback that should be dynamic */

//for event1 the type CallBack should be (user: IUser) => any
use("event1", (user) => { /* check that event1 is used, so only add 1 argument to the callback type  */ })

//for event2 the type CallBack should be (email: string, password: string) => any
use("event2", (email, password) => { /* check that event12is used, so add 2 argument to the callback type */ })

so is there a way to detect which event is used and apply the right type to the callback?

CodePudding user response：

The simplest way to do it is with overloads.

type CallBack = {
  (name: "event1", cb: (u: IUser) => void): void
  (name: "event2", cb: (email:string, pass: string) => void): void
}

let use: CallBack = null!;
//for event1 the type CallBack should be (user: IUser) => any
use("event1", (user) => { /* check that event1 is used, so only add 1 argument to the callback type  */ })

//for event2 the type CallBack should be (email: string, password: string) => any
use("event2", (email, password) => { /* check that event12is used, so add 2 argument to the callback type */ })

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If you have a more complex scenario, such as already having the callbacks in another type, or more complicated conditions, you might consider tuples in rest parameters and conditional types. But from your question, that would be overkill.