CODEWITHSUNDEEP
typescript
Aakash Verma
Aakash Verma

Reputation: 3994

TS function variable args type issue

I have this interface declared:

interface XhrCaller {
    (...args: (string|unknown)[]): Promise<Record<string, unknown>>
}

When I go ahead to define a get fn like

const getCall : XhrCaller = (pathParam: string) => new Promise((resolve, reject) ...

I get an error that says

Type '(pathParam: string) => Promise<Record<string, unknown>' is not assignable to type 'XhrCaller'

Clearly, there is an issue with the way I have declared the interface.

Please help.

Upvotes: 0

Views: 103

Answers (1)

somallg
somallg

Reputation: 2043

Since you have already declare type for XhrCaller, you don't have to annotate pathParam TypeScript already know its type is string|unknown

Link to TS Playground:

interface XhrCaller {
    (...args: (string | unknown)[]): Promise<Record<string, unknown>>
}

const getCall : XhrCaller = (pathParam) => new Promise((resolve, reject) => {
    resolve({ test: 'test' });
});

getCall('abc'); // ok
getCall(123); // ok

Beware that you used unknown and it behaves like any so you lost all type checking when use getCall

getCall('abc'); // ok
getCall(123); // ok

Also, you did declare union type, but that used to check for type when you apply a value like getCall(123) not when you declare.

Your example basically declare another type (pathParam: string) => Promise<unknown> which is not compatible with XhrCaller

const getCall : XhrCaller = (pathParam: string) => new Promise((resolve, reject) => {
    resolve({ test: 'test' });
});

Upvotes: 1

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