Encountering an error with TypeScript generic parameters: Expecting '?' but receiving an error message

Question

Encountering an error with TypeScript generic parameters: Expecting '?' but receiving an error message

As a newcomer to TypeScript, I am currently exploring the use of generic type parameters. I have encountered an error message: '?' expected while working on a function and a type that both require type arguments. The issue seems to be in the

InputProps<T, K extends keyof T>

section of the function.

type InputProps<T, K extends keyof T> = {
    value: T[K]
}

function Input <T, K extends keyof T>({ value } : InputProps<T, K extends keyof T>) : void {
    console.log(value);
}

TS Playground Link

https://i.sstatic.net/HlimC.png

I'm puzzled as to why it is expecting that portion to be a conditional statement. Despite my efforts to search for an explanation, I haven't been able to find a solution. Could someone clarify this for me?

typescript

Answer 1

Answer №1

The K type is already defined in the function signature as K extends keyof T. Simply use K when used in the parameter definition.

function Input <T, K extends keyof T>({ value } : InputProps<T, K>) : void {
    console.log(value);
}

Answer 2

The K type is already defined in the function signature as K extends keyof T. Simply use K when used in the parameter definition.

function Input <T, K extends keyof T>({ value } : InputProps<T, K>) : void {
    console.log(value);
}

Encountering an error with TypeScript generic parameters: Expecting '?' but receiving an error message

Answer №1

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