I am trying to generate a const typed object by passing in a string I want to use as the type, is this possible, I have tried the below and it's bringing out the wrong type.
const test = <T> (name: T) => {
const hi: { name: T } = {
name
} as const
return hi
}
const test1 = test('hello')
I'd like this to be of type
{
name: 'hello';
}
But instead it's of type
{
name: string;
}
In order to infer literal type of an argument, usually you need to add appropriate constraint to your generic argument. See this example:
function test<T extends string>(name: T) {
return { name };
}
const test1 = test('hello') // {name:"hello"}
If you are interested in more examples, you can check my article
If you want to add some validation, you can use conditional type:
// Forbids using underscore as a prefix
type IsAllowed<T extends string> = T extends `_${string}` ? never : T
function foo<T extends string>(name: IsAllowed<T>) {
return { name };
}
const test1 = foo('hello') // ok
const test2 = foo('_hello') // expected error
Or you may use this utility type :
type IsLiteral<T extends string> = T extends string ? string extends T ? never : T : never
function test<T extends string>(name: IsLiteral<T>) {
return { name };
}
If you want to allow only string literals