extends _ = _ syntax in typescript

Question

I recently saw this syntax here

export interface ActionReducer<T, V extends Action = Action> {
  (state: T | undefined, action: V): T;
}

I am confused about the syntax <T,V extends Action = Action>

I could not find documentation for this syntax in typescript . Can anyone point me there . It looks like a new syntax as my build is not able to recognize it and gives me this error :

node_modules/@ngrx/store/src/models.d.ts:6:52: ',' expected.

Vamshi · Accepted Answer · 2019-11-12 03:32:07Z

2

Generic Parameter Defaults

Checked all versions one by one and figured out this is added in version 2.3 It specifies the default type of V . so V can be either a class which extends Action or if not mentioned will be of type Action.

Doc

edited Nov 12, 2019 at 3:32

answered Jul 25, 2017 at 10:26

Vamshi

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Generic Parameter Defaults

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