CODEWITHSUNDEEP
typescript
lifeiscontent
lifeiscontent

Reputation: 593

How do I get typescript to stop complaining about static members on a function?

my example pretty much explains the issue.

but basically, I'm trying to understand how to write valid typescript when adding static members to a function in the code below 

export const ZoomPanelControl = (props) => undefined;
ZoomPanelControl.Item = (props) => undefined;

link for fiddle

Upvotes: 0

Views: 55

Answers (2)

Fenton
Fenton

Reputation: 250872

If you need "a gap" between defining the function and assigning the properties, you can use a type assertion:

type Example = {
    (props: any): any;
    [key: string]: (props: any) => any;
}

const ZoomPanelControl = <Example>((props) => undefined);

//...

ZoomPanelControl.Item = (props) => undefined;

You could place the type within the type assertion, but that's one heck of a line of code to read, which is why I pulled it out into the Example type instead.

The compiler still makes a general check of ((props) => undefined) against the the signature of the Example type - so there is type safety in there as opposed to one common alternative:

const ZoomPanelControl: Example = <any>((props) => undefined);

And you can limit it to known members, if you don't want to allow "any string as a key"...

type Example = {
    (props: any): any;
    Item: (props: any) => any;
}

If you are setting this up in one hit, jcalz answer has the benefit of type-inference (it effectively gives you the type in my last code block, but for free).

Upvotes: 0

jcalz
jcalz

Reputation: 327819

The most straightforward way to add a property to a function is to use Object.assign() to create the function-with-property in a single statement:

export const ZoomPanelControl = Object.assign(
    (props) => undefined,
    { Item: (props) => undefined }
);

This produces an object of type ((props: any) => any) & { Item: (props: any) => any; }, which is what you want:

ZoomPanelControl(123); // okay
ZoomPanelControl.Item(456); // okay

Good luck!

Upvotes: 1

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