JCVD

Javascript Can Validate Data

Runtime type validation with descriptive error paths. Compose predicates from libraries like check-types or prettycats, or write your own.

const {
  isObjectOf,
  isArrayOf,
  isOptional,
  isRequired
} = require('jcvd');

const isString = isRequired(n => typeof n === 'string');
const isNumber = isRequired(n => typeof n === 'number');

const isAddress = isPartialObjectOf({
  street      : isString,
  houseNumber : isNumber
});

const isMyType = isPartialObjectOf({
  foo       : isOptional(isString),
  bar       : isNumber,
  arr       : isArrayOf(isNumber),
  addresses : isOptional(isArrayOf(isAddress))
});

isMyType({
  foo       : 'derp',
  bar       : 3,
  arr       : [3, 3],
  addresses : [
    {
      street      : 'penny lane',
      houseNumber : '13' // <- should be a number
    }
  ]
});

// Throws: 'addresses [0] houseNumber invalid'

JCVD ships both a CommonJS and an ES module build, so import works too:

import { isObjectOf, isArrayOf, isOptional, isRequired } from 'jcvd';

Interface

• Schema Validators
• Predicate Modifiers
• Utilities
• Custom Errors

Schema Validators

isObjectOf

Schema → Object → Boolean | throws

Creates a strict validator — rejects objects containing keys not defined in the schema.

const isAddress = isObjectOf({
  street : isRequired(v => typeof v === 'string'),
  number : isRequired(v => typeof v === 'number')
});

isAddress({ street : 'penny lane', number : 13 }); // true
isAddress({ street : 'penny lane' });               // throws 'number -> missing'
isAddress({ street : 'penny lane', number : 13, foo : 'bar' }); // throws 'foo -> unsupported'
isAddress(undefined);                                // throws 'missing'
isAddress('foo');                                    // throws 'invalid'

---

isPartialObjectOf

Schema → Object → Boolean | throws

Creates a lenient validator — allows extra keys not defined in the schema.

const isAddress = isPartialObjectOf({
  street : isRequired(v => typeof v === 'string')
});

isAddress({ street : 'penny lane', number : 13 }); // true (extra keys OK)
isAddress(undefined);                                // throws 'missing'
isAddress([]);                                       // throws 'invalid'
isAddress(123);                                      // throws 'invalid'

---

isArrayOf

Predicate → Array → Boolean | throws

Validates every element in an array against a predicate. Returns the index of the failing element in the error path.

const isNumbers = isArrayOf(v => typeof v === 'number');

isNumbers([1, 2, 3]);       // true
isNumbers([1, 'two', 3]);   // throws '[1] invalid'
isNumbers(undefined);        // throws 'missing'
isNumbers('foo');            // throws 'invalid'

Predicate Modifiers

isRequired

Predicate → Value → Boolean | throws

Wraps a predicate to reject null and undefined before delegating.

const isString = isRequired(v => typeof v === 'string');

isString('hello'); // true
isString(123);     // false
isString(null);    // throws 'missing'
isString(undefined); // throws 'missing'

---

isOptional

Predicate → Value → Boolean

Wraps a predicate to accept null and undefined without delegating.

const isString = v => typeof v === 'string';
const maybeString = isOptional(isString);

maybeString('hello'); // true
maybeString(null);    // true (skips predicate)
maybeString(undefined); // true (skips predicate)
maybeString(123);     // false

Utilities

label

String → Predicate → Value → Value | throws

Prefixes error messages with a label. Allows nesting validators without losing context. Returns the original value when validation passes (useful for tap flow).

const isAddress = isPartialObjectOf({
  street : isRequired(v => typeof v === 'string'),
  number : isRequired(v => typeof v === 'number')
});

const checkAddress = label('home', isAddress);

checkAddress({ street : 'penny lane', number : 13 }); // returns the object
checkAddress({ street : 'penny lane' });               // throws 'home -> number -> missing'

// Tap-flow example
const value = { street : 'penny lane', number : 13 };
const validated = label('home', isAddress)(value); // validated === value

Custom Errors

customErrors

Handlers → { isObjectOf, isPartialObjectOf, isArrayOf, isRequired, isOptional, label }

Creates a new set of validators with custom error handlers. Each handler must be a function that returns an Error.

const {
  isObjectOf,
  isArrayOf,
  isRequired
} = customErrors({
  handleInvalid     : () => new Error('nope'),
  handleMissing     : () => new Error('missing'),
  handleUnsupported : () => new Error('forbidden')
});

const isString = isRequired(v => typeof v === 'string');

const isCar = isObjectOf({
  wheels : isArrayOf(isString)
});

isCar({ wheels : ['left', 3] });
// throws 'wheels [1] nope'

isCar({ wheels : ['left'], extra : 'key' });
// throws 'extra -> forbidden'

---

CHANGELOG

• 1.0.0 - initial commit
• 1.0.1 - fork from nested-validate with the latest improvements
• 1.0.2 - update tests
• 1.0.3 - return true for passing isArrayOf
• 1.0.4 - update readme
• 1.0.5 - make isOptional consider both null and undefined as missing
• 1.1.0 - label now returns value instead of true for tap flow
• 1.1.1 - clean code semantics
• 1.1.2 - change map to forEach in getOwnPropertyNames
• 1.1.3 - update readme
• 1.1.4 - make isRequired consider both null and undefined as missing
• 2.0.0 - port to TypeScript