Reuse a function type's argument definition

Question

In typescript is there a way to reuse parameter types as follows:

interface Box {
    create: (paramToReuse: (value: any) => void) => void
}
// is there a way to reference paramToResuse as a type? e.g.
let x: Box['create']['paramToReuse']

This can be done the other way around: by first defining paramToReuse and then referencing it in Box's interface, but can it be done the way I've shown above?

Nicholas Tower · Accepted Answer · 2021-12-28 03:58:03Z

5

If it's acceptable to reference it by its parameter index (0) instead of its name ("paramToUse"), that can be done with the helper type Parameters, which takes a function and turns it into a tuple of its parameters:

interface Box {
    create: (paramToReuse: (value: any) => void) => void
}

let x: Parameters<Box["create"]>[0] // x is of type (value: any) => void

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answered Dec 28, 2021 at 3:58

Nicholas Tower

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1 Comment

TrevTheDev Over a year ago

Awesome - that works - thank you!

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