Further validation for optional fields

[ivan-suhorukov]

Hello! I'm trying to make optional validation of file this way:

const schema = v.object({
  file: v.pipe(
    v.optional(v.file()),
    v.notSize(0, messages.requiredFile),
    v.maxSize(Number.parseInt(window.lkConfig.uploadsMaxSize) * 1024 * 1024)
  ),
})

But typescript shows error on line v.notSize(0, messages.requiredFile) with message Type 'undefined' is not assignable to type 'File'. This not happen then i remove "optional()". So how can i validate size of file only then it defined?

[dosubot[bot]]

Hi @ivan-suhorukov! I'm Dosu and I’m helping the valibot team.

The fix is to place v.pipe() inside v.optional() rather than wrapping v.optional() inside v.pipe():

const schema = v.object({
  file: v.optional(
    v.pipe(
      v.file(),
      v.notSize(0, messages.requiredFile),
      v.maxSize(Number.parseInt(window.lkConfig.uploadsMaxSize) * 1024 * 1024)
    )
  ),
})

When the field is undefined (missing), v.optional() returns early and skips the inner schema entirely [1], so notSize and maxSize won't run. When a file is provided, the full pipe executes against the File value, so TypeScript is happy and validation works as expected [2].

To reply, just mention @dosu.

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[ivan-suhorukov]

Oh, its true. My mistake is in another place. When file is not chosen, FormData returns File with zero length instead of undefined, so my pipeline works not as expected. Thanx.