Can a method be limited to only values in a lookup object?

[final mesa]

I've got an like this

export const ids = {
  foo: 'this-is-foo',
  bar: 'this-is-bar',
}

Is there any way for me to define a function that only accepts 'this-is-foo' or 'this-is-bar' as parameters (or any other value stored in the lookup object).

I've tried this but it only accepts foo or bar. And while that's a good restriction for the IDE, my intent is to call the method like so someMethod(ids.foo) and not someMethod('foo') .

/** @param {keyof ids} id */
const someMethod(id) {...}

Is there any way to do this via typescript?

[kind blaze]

yes, pretty easy

you start with the object

export const ids = {
    foo: "this-is-foo",
    bar: "this-is-bar",
} as const;

you then take it's type

typeof ids

and you access it's values using indexed access

!hb indexed access

[weary skiff]

Handbook

Indexed Access Types

[kind blaze]

type IDs = (typeof ids)[keyof typeof ids];

putting it all together

export const ids = {
    foo: "this-is-foo",
    bar: "this-is-bar",
} as const;

type IDs = (typeof ids)[keyof typeof ids];
//   ^?

function f(value: IDs) {}

f("this-is-bar");
f("this-is-foo");
f("some other key");

!ts

[weary skiff]

export const ids = {
    foo: "this-is-foo",
    bar: "this-is-bar",
} as const;

type IDs = (typeof ids)[keyof typeof ids];
//   ^? - type IDs = "this-is-foo" | "this-is-bar"

function f(value: IDs) {}

f("this-is-bar");
f("this-is-foo");
f("some other key");
//^^^^^^^^^^^^^^^^
// Argument of type '"some other key"' is not assignable to parameter of type 'IDs'.

[kind blaze]

@final mesa

[final mesa]

Awesome, thanks. This appears to be the equivalent for jsdoc

// parenthesis around definition for const types are required
export const ids = /** @type {const} */ ({
    foo: "this-is-foo",
    bar: "this-is-bar",
});

/**
* @template {(typeof ids)[keyof typeof ids]} Id
* @param {Id} id
*/
const someMethod(id) {...}