typescript 可以在没有`as const`的情况下推断字符串文字类型

Question

In order for js to use the api well, how to make the compiler infer "bar" type instead of string without using as const .

declare function define<T>(
  options: {
    foo: string;
    bar: T;
  }
): void;

declare function create<T>( cmd: T ): T;

define( {
  foo: "foo",
  bar: create( "bar" ) // It still string, instead of "bar"
} );

playground

Answer 1

As mentioned in this answer , a util type can help:

type StringLiteral<T> = T extends string ? string extends T ? never : T : never;

declare function define<T>(
  options: {
    foo: string;
    bar: StringLiteral<T>;
  }
): void;