[Suggestion] Stricter boolean coerce option

Since we’re currently using Svelte Kit with form actions that make heavy use of the FormData browser api, the new Zod 3.20 release is a very much welcome improvement, specifically the new coercion functionality (since all form post values are serialized as strings over the wire).

One suggestion/request I have is to allow boolean coerce to take a strict option that would check for explicit boolean strings:

Current:

const schema = z.coerce.boolean();
schema.parse("true"); // => true
schema.parse("false"); // => true

Suggestion:

const schema = z.coerce.boolean({ strict: true });
schema.parse("true"); // => true
schema.parse("false"); // => false
schema.parse("123"); // => ZodError

[kibertoad]

It is supported since Node 18.0.0 (see https://developer.mozilla.org/en-US/docs/Web/API/FormData)

[colinhacks]

Ah good catch.

@pheuter want to try to propose an API/behavior that would work for you? I’ve never gotten very far here. Some open questions:

• The set of input types that need to be supported
• Whether to call .get vs .getAll on a given field
• Whether to JSON.parse the value
• Special FormData coercion? Should "on" be converted to true?