n4s

n4s (enforce)

enforce is Vest's standalone assertion library. It powers Vest's validations and can be used directly to express fluent, chainable rules for any data structure.

Quick start

npm i n4s

import { enforce } from 'n4s';

enforce('hello').isString().longerThan(2);
enforce(7).isNumber().greaterThan(2).lessThanOrEquals(10);

Every rule throws when the assertion fails. Chain as many rules as you need; execution stops on the first failing rule.

Lazy mode

If you prefer to inspect results without throwing, build a chain and call .run(value):

const numberCheck = enforce.isNumber().greaterThan(0);

const ok = numberCheck.run(5); // { pass: true, type: 5 }
const bad = numberCheck.run('5'); // { pass: false, type: '5' }

Built-in rules

Rules cover common types and comparisons:

• Equality: equals, notEquals, numberEquals, numberNotEquals.
• Presence: isEmpty, isNotEmpty, isBlank, isNotBlank, isNullish, isNotNullish.
• Type checks: isArray, isBoolean, isNumber, isString, isNaN, plus negated forms.
• Comparisons: greaterThan, greaterThanOrEquals, lessThan, lessThanOrEquals, between, notBetween, longerThan, shorterThan, lengthEquals, lengthNotEquals.
• String helpers: startsWith, doesNotStartWith, endsWith, doesNotEndWith, matches, notMatches.
• Collections: includes, inside, notInside, isKeyOf, isValueOf.
• Booleans and truthiness: isTruthy, isFalsy, isTrue, isFalse.
• Numeric sanity: isPositive, isNegative, isEven, isOdd, isNumeric.

Plugins add higher-level checks such as isEmail and date helpers (isDate, isAfter, isBefore, isISO8601).

Custom rules

Extend enforce with your own assertions using enforce.extend.

import { enforce } from 'n4s';

enforce.extend({
  isBetweenExclusive: (value, min, max) => ({
    pass: value > min && value < max,
    message: () => `${value} must be between ${min} and ${max}`,
  }),
});

enforce(10).isBetweenExclusive(5, 15);

Rules can return a boolean or an object with { pass, message }. Custom rules work in both throwing and lazy (.run) modes.

Composing rules

Use compound helpers to combine conditions without writing new functions:

enforce.allOf(enforce.isString(), enforce.longerThan(2)).run('Vest'); // pass: true

enforce.anyOf(enforce.equals('foo'), enforce.equals('bar')).run('bar');

allOf, anyOf, and noneOf evaluate other rules and return a single result, enabling reusable rule sets.

Using with Vest

When imported from vest, enforce integrates with Vest tests, but it remains a standalone utility you can use anywhere you need fast, expressive assertions.