Warning - Cannot invoke an expression whose type lacks a call signature

Question

I have the following code:

export interface IStartCreate1 {
  (desc?: string, opts?: IDescribeOpts, arr?: Array<string | IDescribeOpts | TCreateHook>, fn?: TCreateHook): void;
  tooLate?: boolean;
}

export interface IStartCreate2 {
  (opts?: IDescribeOpts, arr?: Array<string | IDescribeOpts | TCreateHook>, fn?: TCreateHook): void;
  tooLate?: boolean;
}

export interface IStartCreate3 {
  (arr?: Array<string | IDescribeOpts | TCreateHook>, fn?: TCreateHook): void;
  tooLate?: boolean;
}

export interface IStartCreate4 {
  (fn: TCreateHook): void;
  tooLate?: boolean;
}

export type IStartCreate = IStartCreate1 | IStartCreate2 | IStartCreate3 | IStartCreate4;

Then I have an object like so:

const v = {
  create: function(){} as IStartCreate
} 

v.create([]);

I get this error message:

Cannot invoke an expression whose type lacks a call signature.

I would think an empty array would match IStartCreate3

I have looked at other SO questions with a similar error message and I cannot figure this one out!

This seems to describe the problem: github.com/Microsoft/TypeScript/issues/7294 — Alexander Mills

Alexander Mills Alexander Mills · Accepted Answer · 2017-11-26T05:31:42

As of 2017, looks like union types cannot have a call signature:

https://github.com/Microsoft/TypeScript/issues/7294

Seems pretty lame.

So I had to do away with the union type and do it a different way, looks like this:

export type TArray = Array<string | IDescribeOpts | TCreateHook>;

export interface IStartCreate {
  (desc: string | IDescribeOpts | TCreateHook | TArray,
   opts?: IDescribeOpts | TCreateHook | TArray,
   arr?: TArray | TCreateHook,
   ): void;
  tooLate?: boolean;
}

Warning - Cannot invoke an expression whose type lacks a call signature

2 Answers