Let's say I have a function:
function myFunc(name: string, age: number){ }
To obtain the parameters of a function type in a tuple, I do the following:
type TArgs = Parameters<typeof myFunc> // = [name: string, age: number]
Now I need to create an object type from this tuple as shown below:
type TObj = {
name: string,
age: number
}
How can I do this?
As the Typescript Whisperers in the comments have pointed out, You Can't Do This. I am writing this answer
to help other mortals like me who get confused by the Parameter<> utility's labeled tuple [name: string, age: number] output.
At first glance it seems we should be able to reverse engineer key-value pairs from the tooltip output [name: string, age: number].
Alas, no. After all [name: string, age: number] is a labeled version of the tuple [string, number]. Hopes dashed.
labels don’t require us to name our variables differently when destructuring. They’re purely there for documentation and tooling.
Here are some demonstrations: (Playground)
const iAmTArgs: TArgs = ["myString", 0] // Passes: type really is [string, number]
const iAmNotTArgs: TArgs = [0, 0] // Error, as expected: Type 'number' is not assignable to type 'string'
type NameArg = Parameters<typeof myFunc>[0] // string
