Typescript widening object properties of Zod enum type to string

If I define enum and use it in the object, the object property still has the type of the enum:

enum A { a = "a" }

const a = { a: A.a }
// type of a is { a: A }

However, if I define the same enum using zod, the type of object property is string and not narrowed to enum anymore.

const A = z.enum(["a"])

const a = { a: A.a }
// type of a is { a: string }

[maxArturo]

Hi @elemti , I wonder if you have usecases where you need to define a schema in-line with an object? (such as below)

const b = { x: z.enum([‘A’, ‘B’]).parse(123), }; // type of b is { x: string; }

I agree its surprising that TS will widen the type to string inside an object, I’m curious about that and will look at it… but if you can use z.object() for the entire object then it will work as expected:

  const main = z.object({
    x: z.enum(["A", "B"]),
  });

  type testType = z.infer<typeof main>;
  /**
    type testType = {
      x: "A" | "B";
    }
   */

@akoltun I took a look at the implementation, and except for the way the enums are stored and checked (an object for nativeEnum and an array for Enum) there’s not that much difference - for compatibility as the README says if I took a guess. Would love for someone more knowledgeable to chime in!

[elemti]

hi @maxArturo , usually I run into this problem when trying to use .transform() to enhance an object

const schema = z
  .object({
    x: z.enum(['A', 'B']),
  })
  .transform((it) => {
    // do transformations...
    return {
      ...it,
      // "y" will be dependent on "x" in some way
      y: z.enum(['A', 'B']).parse(it.x),
    };
  });
const enhancedObj = schema.parse({});
/*
  const enhancedObj: {
    y: string;
    x: "A" | "B";
  }
*/

I wonder if there’s any better way to enhance / add new keys to an object instead of doing this?