assumed

Fast and very versatile asserter

Quick guide: pick a primitive, then chain

Start by choosing the primitive guard that matches your value. That unlocks focused methods:

• that(x).isString() → notEmpty, minLength, contains, matches, …
• that(x).isNumber() → greaterThan, between, …
• that(x).isArray() → notEmpty, hasLength, itemIsString, onlyHasNumbers, …
• that(x).isObject() → hasKey, hasKeys, keyEquals, sameKeys, …
• that(x).isDate() → earlier, later, isYear, daysSinceAtLeast, …

Example:

const id = that(input.id) .isString("id must be string") .minLength(3) .commit();

Passing functions: shapes spelled out

Many APIs take functions; here’s what they expect:

• assuming(...).Run(fn)

  • fn: () => R
  • Runs only when assumptions pass; result captured by value().

• assuming(...).onRefuted(fn)

  • fn: (err?: unknown) => unknown
  • Runs only on failure; its return captured by value().

• assuming(...).result(success, failure?)

  • success: () => R
  • failure?: (err?: unknown) => R

• assuming(...).emitOn(condition, event, data?)

  • condition: boolean | () => boolean
  • event: string
  • data?: unknown | () => unknown

assumedRoute: your using-block wrapper

Wrap a handler and always return a safe default value if an error occurs. No custom error callback needed.

// sync const safeAdd = assumedRoute(0, (a: unknown, b: unknown) => that(a).isNumber().commit() + that(b).isNumber().commit() ); safeAdd(1, 2); // 3 safeAdd(1, undefined); // 0 (default)

// async const safeFetch = assumedRoute({ ok: false }, async (id: unknown) => { that(id).isString().minLength(3).commit(); return fetchThing(id); }); await safeFetch("x"); // { ok: false }