justin

a typescript data validation library utilizing just-in-time function compilation.

available on jsr.io.

features

dependency-free
small bundle size (pay for what you use, ranges from sub-1kb to 4kb)
low-allocation design
much faster than validation via interpreting schema objects
- according to bench/speed.ts, 10×-20× faster than zod v4 mini

limitations

since all checks are inlined, we do not support circular schemas
- you probably want to use j.unknown and reapply the validator function to the member object
transformation is not supported since we return the exact same object that was passed in
compilation is very slow, so ad-hoc construction of schemata is considered an anti-pattern

example

import * as j from "@char/justin";

const PersonSchema = j.obj({
  fullName: j.string,
  preferredName: j.string,
  i18nInflection: j.optional(
    j.union(j.literal("masculine"), j.literal("feminine"), j.literal("neutral")),
  ),
});

type Person = j.Infer<typeof PersonSchema>;
/* ⇒ {
    fullName: string;
    preferredName: string;
    i18nInflection?: "masculine" | "feminine" | "neutral" | undefined;
} */

const validator = j.compile(PersonSchema);
const { value: person, errors: personErrors } = validator({
  fullName: "Guy Jones",
  preferredName: "guy",
  i18nInflection: "masculine",
});
// person: passed through verbatim, personErrors: undefined

const { errors } = validator({
  fullName: "Guy Jones",
});
// errors: [ { path: ".preferredName", msg: "must be string" } ]

char/justin

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