input-validator

npm install @ferrow/input-validator

A rule-string validation engine for TypeScript/Node — Laravel-style rule strings ("required|number|min:18|max:120"), nested object schemas, array item validation, custom rule registration, and full error collection (not just the first failure) with dot/bracket field paths. Zero runtime dependencies.

Install

Copy src/index.ts into your project, or build this repo (npm run build) and depend on the compiled dist/.

Quickstart

import { validate } from 'input-validator';

const schema = {
  name: 'required|string|length:2,50',
  email: 'required|email',
  age: 'number|min:18|max:120',
};

const { valid, errors } = validate(schema, { name: 'A', email: 'bad', age: 15 });
// valid: false
// errors: [
//   { path: 'name', message: 'name must have length >= 2' },
//   { path: 'email', message: 'email must be a valid email' },
//   { path: 'age', message: 'age must be >= 18' },
// ]

Or use the class form to reuse one schema:

import { InputValidator } from 'input-validator';
const validator = new InputValidator(schema);
validator.validate(payload);

Built-in rules

required · string · number · boolean · email · min:N (numeric >= N, or string length >= N) · max:N (numeric <= N, or string length <= N) · length:min,max (string length range) · in:a,b,c (must equal one of the comma-separated values) · regex:pattern (tested with new RegExp(pattern))

A field without required is skipped entirely (no errors) when its value is undefined, null, or ''.

Nested schemas and arrays

const schema = {
  address: { schema: { city: 'required|string', zip: 'regex:^[0-9]{5}$' } },
  tags: { array: 'string' },                              // array of primitives
  friends: { arraySchema: { name: 'required|string' } },  // array of objects
};

Error paths reflect nesting: address.city, friends[0].name.

Custom rules

import { registerRule } from 'input-validator';

registerRule('even', (value) => (typeof value === 'number' && value % 2 === 0 ? null : 'must be even'));
validate({ n: 'number|even' }, { n: 3 }); // { valid: false, errors: [{ path: 'n', message: 'n must be even' }] }

registerRule is global — it adds the rule name for every schema in the process, matching how the built-in rules are registered.

Scope and limits

• Rule arguments are always plain strings (min:18, in:a,b,c) — no cross-field rules (e.g. "must equal another field") are built in; write a custom rule with access to the full record via the third data argument passed to RuleFn if you need that.
• regex: rule arguments cannot contain a literal | (the rule-string delimiter) or : beyond the first — for complex patterns, register a custom rule instead of using the regex: shorthand.
• Not a coercion/transform library — it validates the value as given, it doesn't parse strings into numbers/booleans for you first.

Sponsored by Ferrow

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Part of the ferrow-toolkit collection · Sponsored by Ferrow