How to tell apart Type from Function?

Question

I have an argument of type

((element: any) => Type<any>) | Type<any>

and if it is a Function i need to call it, other wise just use the Type as-is

getType(element: any, type: ((element: any) => Type<any>) | Type<any>): Type<any> { return isFunctionNotType(type) ? type(element) : type; }

Unfortunately I am not sure how to write the isFunctionNotType method. There is an isType method in @angular/core/src/type but whenever I try using that I get the following error during compilation

ERROR in C:/Users/xxxxxx/xxxxxx/xxxxxx/dist/xxxxxx/fesm5/angular-utils.js Module not found: Error: Can't resolve '@angular/core/src/type' in 'C:\Users\xxxxxx\xxxxxx\xxxxxx\dist\xxxxxx\fesm5'

Is there some way to get this working without having to break up the type variable into two?

EDIT: I should point out since people seem to be missing the point here. In angular Type extends Function, and at run-time you will not be able to tell them apart just by doing an instanceof or something like that.

I don't think Angular should be the resource for type-checking, especially since you're already using Typescript. Either use the instanceof operator, or do some kind of duck-typing using a function that returns Type is SpecificType, which will satisfy the compiler. See this question for more info. — Enioluwa Segun
– Enioluwa Segun, Commented Aug 22, 2019 at 17:46

timi95 · Accepted Answer · 2019-08-22 17:58:26Z

0

(typeof callback === "function")

I would check if its a function, then do something for the other type with an 'else'.

answered Aug 22, 2019 at 17:58

timi95

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Richard Haddad · Accepted Answer · 2019-08-22 18:20:58Z

type TypeFn<T> = (element: T) => Type<T>; function isFunctionNotType<T>(type: TypeFn<T> | Type<T>): type is TypeFn<T> { return typeof type === 'function'; } function getType<T>(element: T, type: TypeFn<T> | Type<T>): Type<T> { return isFunctionNotType(type) ? type(element) : type; }

isFunctionNotType return type type is TypeFn<T> give a boolean AND will infer the return type.

Note that I added generics, it may be inappropriate so remove them in this case.

Unfortunately typeof SomeType returns "function" since Type extends Function (I am talking about the Type interface from @angular/core)
I see, so there is no clean way to do the check. A solution may be to wrap TypeFn in an object, or anything that could disting its.

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