z.enum for as const numbers?

This works nicely:

const VALUES = ["Salmon", "Tuna", "Trout"] as const;
const FishEnum = z.enum(VALUES);
// 'Salmon' | 'Tuna' | 'Trout'

But this does not work:

const VALUES = [1, 2, 3] as const;
const OrderEnum = z.enum(VALUES);
// 1 | 2 | 3

This is due to the requirement of having an array of strings, although a union of numbers work.

Thoughts?

[colinhacks]

Enums should never be numbers. By default enum values in TypeScript are numbers, but this is a footgun and an antipattern.

enum Color { Red, Green };
Color.Red; // 0

If you add another color the actual under-the-hood value changes:

enum Color { Blue, Red, Green };
Color.Red; // 1

Which is the source of a lot of bugs and confusion. So Zod forces you to use strings.

This also lets you access the elements of the enum like so:

const Color = z.enum(["Red", "Green"]);
Color.enum.Red; // "Red"

Which is importany, and wouldn’t be possible with numbers.

I recommend writing a generic function that accepts a list of numbers and exports a z.custom schema:

const numberEnum = <Num extends number, T extends Readonly<Num[]>>(
  args: T
): z.ZodSchema<T[number]> => {
  return z.custom<T[number]>((val: any) => args.includes(val));
};

const nums = [1, 2, 3] as const;
const schema = numberEnum(nums);

[diogoazevedos]

@colinhacks this feature would increase the parity with the native TypeScript enum. Also would allow validation of a specific set of numbers.

I know it’s possible to achieve the same validation using union, but the error is not as descriptive.

Numbers seem to be already supported, so it’s a matter of adjusting the types:

https://github.com/colinhacks/zod/blob/ab75f4dad2a6738c019fe4edea6c8603c25ecb18/src/types.ts#L2940-L3012

For those looking for a dirty solution until this be addressed, it’s possible to do the following:

const schema = z.nativeEnum({
  a: 100,
  b: 200,
  c: 300
} as const);