Compiled validation

const selected = JIT.validator(User).get("is", "parse");

selected.is(input);
selected.parse(input);

Selection is explicit: requesting is and parse does not compile serializers, hash functions or unused validator variants.

const isUser = JIT.validate(User).is().compile();
const safeParseUser = JIT.validate(User).safeParse().compile();
const issues = JIT.validate(User).issues().compile();

is is fail-fast and allocation-free on the normal path. safeParse collects stable issues with path, code, expected and message. parse throws JITValidationError. Promise schemas use the asynchronous variants.

The ~standard adapter closes over the compiled safeParse function; it does not run a second generic validator.

Select the smallest operation

Need	Compile	Failure behavior	Happy-path allocation
Boolean gate	`is`	`false` on first mismatch	none
Typed value or exception	`parse`	collects issues, then throws	transform-dependent
Typed result without exception	`safeParse`	issue vector	transform-dependent
Promise schemas	async variants	Promise result/error	async machinery
Consume issue records	`issues`	iterator	validator issue vector

Do not compile safeParse for a hot boolean branch merely because it is the most familiar API. is can return as soon as one cheap check fails.

Issue handling

const result = safeParseUser(input);

if (!result.success) {
  for (const issue of result.issues) {
    fields.set(issue.path, issue.message);
  }
}

Use stable code values for program behavior and custom message text for users. path is a root-relative string suitable for logs/forms.

Transforming parsers

Defaults, coercion, trim/case conversion, masks and pipes make output differ from input. The generated validator tracks whether rebuilding is necessary and returns the original reference when no transform changed the value.

Standard Schema

Frameworks can call schema["~standard"].validate(value). JIT's adapter uses the already compiled validator, so interoperability does not introduce a generic validation layer.

Security notes

Validation proves the declared shape, not authorization or business ownership. Avoid echoing raw received values in public issue messages. Opaque custom predicates should be deterministic and free of side effects because validators may be cached and reused across requests.