Guardz

A comprehensive TypeScript type guard library with advanced validation capabilities, error reporting, and performance optimizations.

🚀 Quick Start

Installation

# npm
npm install guardz

# yarn
yarn add guardz

# pnpm
pnpm add guardz

TypeScript Configuration

Ensure your tsconfig.json includes:

{
  "compilerOptions": {
    "strict": true,
    "noImplicitAny": true,
    "exactOptionalPropertyTypes": true
  }
}

Basic Usage

import { isNonEmptyString, isNumber, isString, isType } from 'guardz';

// Basic guard
const value: unknown = getUnknownValue();
if(isString(value)) {
  // TypeScript now knows value is a string - type narrowing in action
  console.log(value.length); // Safe to access string properties
}

// Simulate getting data from an external source (API, database, etc.)
const maybeUser: unknown = await getUserInfoFromServer();

// Define a type guard for user type checking
const isUser = isType<UserDTO>({
  id: isNumber,
  name: isNonEmptyString,
  email: isNonEmptyString,
});

// Use type guard for type narrowing
if (isUser(maybeUser)) {
  // TypeScript now knows maybeUser is a valid UserDTO
  console.log(maybeUser.id);
  console.log(maybeUser.name);
  console.log(maybeUser.email);
}

🎯 Type Guards vs Validators

Guardz is a type guard library, not a validation library.

Guardz focuses on providing lightweight, composable type guards that enable TypeScript's type narrowing while maintaining excellent performance. For a detailed explanation of the differences between type guards and validators, see this comprehensive guide.

✨ Features

Comprehensive Type Guards: 50+ built-in type guards for all JavaScript types
Advanced Type Narrowing: Array type guards, object type guards, union types, and more
TypeScript Integration: Seamless type narrowing with exact type inference
Performance Optimized: Fast type guards with minimal overhead
TypeScript First: Full type safety with precise type inference
Zero Dependencies: Lightweight with no external dependencies
Tree Shaking: Optimized for bundle size with tree shaking support

📖 Basic Examples

Basic Type Guards

import { isString, isNumber, isBoolean, isSymbol, isArrayWithEachItem, isObject } from 'guardz';

isString('hello');        // true
isNumber(42);             // true
isBoolean(true);          // true
isSymbol(Symbol('a'));    // true
isArrayWithEachItem(isNumber)([1, 2, 3]);     // true
isObject({ a: 1 });       // true

isSymbol Example

import { isSymbol } from 'guardz';

const value: unknown = Symbol('test');
if (isSymbol(value)) {
  // value is now typed as symbol
  console.log(value.toString());
}

Object Type Guards

import { isType, isString, isNumber, isPositiveInteger, isUndefinedOr } from 'guardz';

interface User {
  id: number;
  name: string;
  email: string;
  age?: number;
}

const isUser = isType<User>({
  id: isPositiveInteger,
  name: isString,
  email: isString,
  age: isUndefinedOr(isNumber), // Handle optional property
});

const user = { id: 1, name: 'John', email: 'john@example.com' };
console.log(isUser(user)); // true

Array Type Guards

import { isArrayWithEachItem, isString, isNumber } from 'guardz';

const isStringArray = isArrayWithEachItem(isString);
const isNumberArray = isArrayWithEachItem(isNumber);

console.log(isStringArray(['a', 'b', 'c'])); // true
console.log(isNumberArray([1, 2, 3])); // true

Array Utilities

import { isString, isNumber, isType, by } from 'guardz';

const isUser = isType({ name: isString, age: isNumber });

const users = [
  { name: 'Alice', age: 25 },
  { name: 'Bob', age: '30' }, // invalid
  { name: 'Charlie', age: 35 },
];

// ❌ This won't work due to parameter mismatch
// const validUsers = users.filter(isUser);

// ✅ Use by for simple filtering
const validUsers = users.filter(by(isUser));
console.log('Valid users:', validUsers);

Union Types

import { isOneOfTypes, isString, isNumber, isBoolean } from 'guardz';

const isPrimitive = isOneOfTypes(isString, isNumber, isBoolean);

console.log(isPrimitive('hello')); // true
console.log(isPrimitive(42));      // true
console.log(isPrimitive(true));    // true
console.log(isPrimitive({}));      // false

Error Handling

import { isType, isString, isNumber } from 'guardz';

const errors: string[] = [];
const config = {
  identifier: 'user',
  callbackOnError: (error: string) => errors.push(error),
  errorMode: 'multi', // 'single' | 'multi' | 'json'
};

const isUser = isType({
  name: isString,
  age: isNumber,
});

const invalidUser = { name: 123, age: 'thirty' };
const result = isUser(invalidUser, config);

console.log(result); // false
console.log(errors); // ['user.name: Expected string, got number (123)', 'user.age: Expected number, got string ("thirty")']

Pattern Validation

import { isRegex, isPattern } from 'guardz';
import type { Pattern } from 'guardz';

// Validate RegExp objects
const patterns: unknown[] = [/^[a-z]+$/, new RegExp('\\d+'), 'not a regex'];
patterns.forEach(pattern => {
  if (isRegex(pattern)) {
    console.log(`Valid RegExp: ${pattern.source} (flags: ${pattern.flags})`);
  }
});

// Create branded types for pattern-matched strings
type Email = Pattern<'Email'>;
type PhoneNumber = Pattern<'PhoneNumber'>;
type URL = Pattern<'URL'>;

const isEmail = isPattern<'Email'>(/^[^\s@]+@[^\s@]+\.[^\s@]+$/);
const isPhoneNumber = isPattern<'PhoneNumber'>('^\\+?[\\d\\s\\-()]{10,}$');
const isUrl = isPattern<'URL'>('^https?:\\/\\/.+');

// Validate strings against patterns
const email: unknown = 'user@example.com';
if (isEmail(email)) {
  // email is now typed as Email (branded string)
  console.log(`Valid email: ${email}`);
}

const phone: unknown = '+1-555-123-4567';
if (isPhoneNumber(phone)) {
  // phone is now typed as PhoneNumber (branded string)
  console.log(`Valid phone: ${phone}`);
}

// Type safety with branded types
function processEmail(email: Email) {
  // This function only accepts validated email strings
  console.log(`Processing email: ${email}`);
}

function processPhoneNumber(phone: PhoneNumber) {
  // This function only accepts validated phone number strings
  console.log(`Processing phone: ${phone}`);
}

// These work with type safety:
const validEmail: unknown = 'user@example.com';
if (isEmail(validEmail)) {
  processEmail(validEmail); // TypeScript knows this is safe
}

// These would cause TypeScript errors:
// processEmail('invalid-email'); // Error: Argument of type 'string' is not assignable to parameter of type 'Email'
// processPhoneNumber('123'); // Error: Argument of type 'string' is not assignable to parameter of type 'PhoneNumber'

🎯 Common Use Cases

API Response Validation

import { isType, isString, isNumber, isArrayWithEachItem, isOneOf } from 'guardz';

interface ApiResponse<T> {
  data: T;
  status: 'success' | 'error';
  message: string;
  timestamp: number;
}

const isUserResponse = isType<ApiResponse<User>>({
  data: isType({
    id: isNumber,
    name: isString,
    email: isString,
  }),
  status: isOneOf('success', 'error'), // Use isOneOf for exact values
  message: isString,
  timestamp: isNumber,
});

// Validate API responses
const response = await fetch('/api/users/1');
const data = await response.json();

if (isUserResponse(data)) {
  console.log('Valid user:', data.data.name);
} else {
  console.log('Invalid response format');
}

Form Data Validation

import { isType, isString, isNumber, isPositiveInteger } from 'guardz';

interface RegistrationForm {
  username: string;
  email: string;
  age: number;
  password: string;
}

const isRegistrationForm = isType<RegistrationForm>({
  username: isString,
  email: isString, // Could add email regex validation
  age: isPositiveInteger,
  password: isString,
});

const formData = {
  username: 'john_doe',
  email: 'john@example.com',
  age: 25,
  password: 'secure123',
};

if (isRegistrationForm(formData)) {
  // Process valid form data
  await registerUser(formData);
} else {
  // Handle validation errors
  showValidationErrors(errors);
}

Database Result Validation

import { isType, isString, isNumber, isDate } from 'guardz';

interface DatabaseUser {
  id: number;
  username: string;
  email: string;
  created_at: string;
  updated_at: string;
}

const isDatabaseUser = isType<DatabaseUser>({
  id: isNumber,
  username: isString,
  email: isString,
  created_at: isString,
  updated_at: isString,
});

// Validate database results
const users = await db.query('SELECT * FROM users');
const validUsers = users.filter(isDatabaseUser);

Configuration Validation

import { isType, isString, isNumber, isBoolean } from 'guardz';

interface AppConfig {
  port: number;
  database: {
    host: string;
    port: number;
    name: string;
  };
  features: {
    auth: boolean;
    caching: boolean;
  };
}

const isAppConfig = isType<AppConfig>({
  port: isNumber,
  database: isType({
    host: isString,
    port: isNumber,
    name: isString,
  }),
  features: isType({
    auth: isBoolean,
    caching: isBoolean,
  }),
});

// Validate environment configuration
const config = {
  port: process.env.PORT ? parseInt(process.env.PORT) : 3000,
  database: {
    host: process.env.DB_HOST || 'localhost',
    port: process.env.DB_PORT ? parseInt(process.env.DB_PORT) : 5432,
    name: process.env.DB_NAME || 'myapp',
  },
  features: {
    auth: process.env.AUTH_ENABLED === 'true',
    caching: process.env.CACHE_ENABLED === 'true',
  },
};

if (!isAppConfig(config)) {
  throw new Error('Invalid configuration');
}

🔧 Advanced Features

Reusable Type Guard Patterns

Create reusable type guard functions for consistent validation patterns:

import { isString, isNumber, isPositiveInteger, isType } from 'guardz';

// Create semantic type guards using existing functions
const isUserId = isPositiveInteger; // Already a reusable type guard
const isEmail = isString; // Already a reusable type guard
const isName = isString; // Already a reusable type guard

// Use them consistently across your application
interface User {
  id: number;        // Uses isUserId (isPositiveInteger)
  name: string;      // Uses isName (isString)
  email: string;     // Uses isEmail (isString)
}

const isUser = isType<User>({
  id: isUserId,
  name: isName,
  email: isEmail,
});

Generic Types

For complex generic types with conditional properties, use factory functions with isType:

import { isType, isString, isNumber, isUndefinedOr } from 'guardz';

// Define generic types with conditional properties
type ApiKeysSelect<T extends boolean = true> = {
  name: T extends true ? string : string | undefined;
  collectionPermissions: T extends true ? string : string | undefined;
  updatedAt: T extends true ? string : string | undefined;
  createdAt: T extends true ? string : string | undefined;
  enableAPIKey: T extends true ? boolean : boolean | undefined;
  apiKey: T extends true ? string : string | undefined;
  apiKeyIndex: T extends true ? number : number | undefined;
};

// Create type guard factory for generic types
export const isApiKeysSelect = <T extends boolean = true>(
  typeGuardT: TypeGuardFn<T>,
): TypeGuardFn<ApiKeysSelect<T>> =>
  isType<ApiKeysSelect<T>>({
    name: isUndefinedOr(typeGuardT),
    collectionPermissions: isUndefinedOr(typeGuardT),
    updatedAt: isUndefinedOr(typeGuardT),
    createdAt: isUndefinedOr(typeGuardT),
    enableAPIKey: isUndefinedOr(typeGuardT),
    apiKey: isUndefinedOr(typeGuardT),
    apiKeyIndex: isUndefinedOr(typeGuardT),
  });

// Usage
const isRequiredApiKeys = isApiKeysSelect(isString);
const isOptionalApiKeys = isApiKeysSelect(isUndefinedOr(isString));

💡 Pro Tip: For complex generic type validation with multiple conditional properties, consider using guardz-generator which automatically generates type guards for generic types and handles conditional properties efficiently.

Advanced Generic Patterns

// Multiple generic parameters
type Container<T, U, V extends boolean = true> = {
  primary: T;
  secondary: U;
  metadata: V extends true ? { timestamp: number; version: string } : undefined;
};

// Factory for multiple generic parameters
export const isContainer = <T, U, V extends boolean = true>(
  primaryGuard: TypeGuardFn<T>,
  secondaryGuard: TypeGuardFn<U>,
  metadataGuard?: TypeGuardFn<{ timestamp: number; version: string }>,
): TypeGuardFn<Container<T, U, V>> =>
  isType<Container<T, U, V>>({
    primary: primaryGuard,
    secondary: secondaryGuard,
    metadata: metadataGuard ? isUndefinedOr(metadataGuard) : undefined,
  });

// Usage
const isStringNumberContainer = isContainer(isString, isNumber);
const isStringNumberContainerWithMetadata = isContainer(
  isString,
  isNumber,
  isType({ timestamp: isNumber, version: isString })
);

Performance Optimizations

import { isType, isString, isNumber, isArrayWithEachItem } from 'guardz';

// Optimized for repeated validation
const isUser = isType({
  id: isNumber,
  name: isString,
  tags: isArrayWithEachItem(isString),
});

// Reuse the same guard instance
const users = [/* large array of user objects */];
const validUsers = users.filter(isUser); // Fast validation

// Use appropriate error modes for performance
const fastConfig = { errorMode: 'single' }; // Fastest
const detailedConfig = { errorMode: 'multi' }; // More detailed
const treeConfig = { errorMode: 'json' }; // Most detailed

🔄 Migration Guide

From Zod

// Zod
import { z } from 'zod';
const UserSchema = z.object({
  id: z.number(),
  name: z.string(),
  email: z.string().email(),
});

// Guardz
import { isType, isNumber, isString } from 'guardz';
const isUser = isType({
  id: isNumber,
  name: isString,
  email: isString, // Add custom email validation if needed
});

From Joi

// Joi
import Joi from 'joi';
const userSchema = Joi.object({
  id: Joi.number().required(),
  name: Joi.string().required(),
  email: Joi.string().email().required(),
});

// Guardz
import { isType, isNumber, isString } from 'guardz';
const isUser = isType({
  id: isNumber,
  name: isString,
  email: isString,
});

From Yup

// Yup
import * as yup from 'yup';
const userSchema = yup.object({
  id: yup.number().required(),
  name: yup.string().required(),
  email: yup.string().email().required(),
});

// Guardz
import { isType, isNumber, isString } from 'guardz';
const isUser = isType({
  id: isNumber,
  name: isString,
  email: isString,
});

🛠️ Troubleshooting

Common Issues

TypeScript Errors

Problem: Type 'unknown' is not assignable to parameter of type 'TypeGuardFn<T>'

Solution: Ensure you're using the correct type guard function:

// ❌ Wrong
const isUser = isType({
  id: isNumber, // This is correct
  name: 'string', // ❌ This is wrong - should be isString
});

// ✅ Correct
const isUser = isType({
  id: isNumber,
  name: isString, // ✅ Use the type guard function
});

Performance Issues

Problem: Validation is slow with large objects

Solution: Use appropriate error modes and optimize validation:

// ❌ Slow - collects all errors
const result = isUser(data, { errorMode: 'multi' });

// ✅ Fast - stops at first error
const result = isUser(data, { errorMode: 'single' });

// ✅ Fastest - no error collection
const result = isUser(data);

Bundle Size Issues

Problem: Large bundle size

Solution: Use tree shaking and import only what you need:

// ❌ Imports everything
import * as guardz from 'guardz';

// ✅ Only imports what you need
import { isType, isString, isNumber } from 'guardz';

Debugging

Enable detailed error reporting:

const errors: string[] = [];
const config = {
  identifier: 'user',
  callbackOnError: (error: string) => {
    errors.push(error);
    console.log('Validation error:', error);
  },
  errorMode: 'multi',
};

const result = isUser(data, config);
console.log('All errors:', errors);

⚡ Performance Tips

Error Mode Selection

single (default): Fastest, stops at first error
multi: Medium speed, collects all errors with details
json: Slowest, provides hierarchical error tree structure

Validation Strategies

// For production - fast validation
const isUserFast = isType({
  id: isNumber,
  name: isString,
  email: isString,
});

// For development - detailed errors
const isUserDev = isType({
  id: isNumber,
  name: isString,
  email: isString,
});

// Usage
const config = process.env.NODE_ENV === 'production' 
  ? undefined 
  : { errorMode: 'multi', callbackOnError: console.error };

Caching Type Guards

// Create type guards once, reuse them
const isUser = isType({
  id: isNumber,
  name: isString,
  email: isString,
});

// Reuse the same guard instance
const validateUsers = (users: unknown[]) => {
  return users.filter(isUser);
};

🔧 API Reference

Primitive Type Guards

isString - Validates that a value is a string
isNumber - Validates that a value is a valid number (excludes NaN)
isBoolean - Validates that a value is a boolean
isBigInt - Validates that a value is a BigInt
isFunction - Validates that a value is a function (including regular functions, arrow functions, class constructors, and methods)
isSymbol - Validates that a value is a Symbol

Special Type Guards

isAsserted - Always returns true and asserts value is T (useful for 3rd party types without runtime validation)
isEnum - Creates a type guard that checks if a value matches any value from an enum
isEqualTo - Creates a type guard that checks if a value is exactly equal to a specific value using strict equality (===)
isRegex - Validates that a value is a RegExp object
isPattern<P> - Creates a type guard that validates strings against a regex pattern and returns a branded type

Array Type Guards

isArrayWithEachItem<T>(typeGuard: TypeGuardFn<T>) - Creates a type guard that validates arrays where each item matches a specific type
isNonEmptyArray - Validates that a value is a non-empty array
isNonEmptyArrayWithEachItem<T>(typeGuard: TypeGuardFn<T>) - Creates a type guard that validates non-empty arrays where each item matches a specific type

Object Type Guards

isNonNullObject - Validates that a value is a non-null object (excludes arrays)
isType<T>(schema: Record<string, TypeGuardFn<any>>) - Creates a type guard that validates objects against a schema
isObject<T>(schema: Record<string, TypeGuardFn<any>>) - Alias for isType - creates a type guard for a specific object shape
isObjectWith<T>(schema: Record<string, TypeGuardFn<any>>) - Alias for isType - validates objects with specific properties
isObjectWithEachItem<T>(typeGuard: TypeGuardFn<T>) - Creates a type guard that validates plain objects where each property value matches a specific type (only checks enumerable own properties)

Number Type Guards

isInteger - Validates that a value is an integer (whole number)
isPositiveInteger - Validates that a value is a positive integer (greater than 0 and a whole number)
isNegativeInteger - Validates that a value is a negative integer (less than 0 and a whole number)
isNonNegativeInteger - Validates that a value is a non-negative integer (0 or greater and a whole number)
isNonPositiveInteger - Validates that a value is a non-positive integer (0 or less and a whole number)
isPositiveNumber - Validates that a value is a positive number (greater than 0)
isNegativeNumber - Validates that a value is a negative number (less than 0)
isNonNegativeNumber - Validates that a value is a non-negative number (0 or greater)
isNonPositiveNumber - Validates that a value is a non-positive number (0 or less)
isNumeric - Validates that a value is numeric (a number or a string that can be converted to a number)
isDateLike - Validates that a value can be treated as a Date (Date object, date string, or numeric timestamp)

String Type Guards

isNonEmptyString - Validates that a value is a non-empty string (trims whitespace, so strings containing only whitespace are considered empty)

Null/Undefined Type Guards

isNil - Validates that a value is null or undefined
isNullOr - Creates a type guard that validates if a value is either null or matches a specific type
isUndefinedOr - Creates a type guard that validates if a value is either undefined or matches a specific type
isNilOr - Creates a type guard that validates if a value is either of type T, null, or undefined

Union Type Guards

isOneOf - Creates a type guard that checks if a value matches one of several specific values using strict equality (===)
isOneOfTypes - Creates a type guard that checks if a value matches at least one of several type guards

Web API Type Guards

isDate - Validates that a value is a valid Date object (excludes invalid dates like new Date("invalid"))
isError - Validates that a value is an Error object
isBlob - Validates that a value is a Blob object
isFile - Validates that a value is a File object
isFileList - Validates that a value is a FileList object
isFormData - Validates that a value is a FormData object
isURL - Validates that a value is a URL object
isURLSearchParams - Validates that a value is a URLSearchParams object

Collection Type Guards

isMap - Validates that a value is a Map object
isSet - Validates that a value is a Set object
isIndexSignature - Creates a type guard that validates objects with index signatures (objects with dynamic keys of a specific type and values of a specific type)

Utility Type Guards

isUnknown - Always returns true (useful for unknown types)
isAny - Always returns true (useful for any types)
isDefined - Validates that a value is defined (not null/undefined)
isBooleanLike - Validates that a value can be treated as a boolean (boolean, "true"/"false", "1"/"0", or 1/0)
isExtensionOf - Creates a type guard for types that extend a base type by combining a base type guard with validation for additional properties (useful for inheritance patterns)
isIntersectionOf - Creates a type guard that validates a value against multiple type guards, ensuring the value satisfies all of them
isPartialOf - Creates a type guard that validates partial objects matching a specific type (allows missing properties)
isTuple - Creates a type guard that validates tuples (fixed-length arrays with specific types at each position)

Schema Type Guards

isSchema - Creates a type guard function for object schemas with improved nested type support (automatically handles nested structures)
isShape - Alias for isSchema
isNestedType - Alias for isSchema

Advanced Type Guards

isBranded - Creates a type guard function for a branded type using a predicate function (validates and narrows to branded types)
guardWithTolerance - Validates data against a type guard but returns the data regardless of validation result (useful for logging errors while proceeding with potentially invalid data)

Type Guard Error Generation

generateTypeGuardError - Generates error messages for type guard failures

Utility Types

PredicateFn - A predicate function that validates a value and returns true if valid, false otherwise

Type Converters

toNumber - Converts a Numeric value to a number (safely converts validated numeric values)
toDate - Converts a DateLike value to a Date object (safely converts validated date values)
toBoolean - Converts a BooleanLike value to a boolean (safely converts validated boolean values)

Validation Types

ValidationError - Error type for validation failures with path, expected type, actual value, and message
ValidationTree - Tree structure for hierarchical validation errors
ValidationResult - Result type for validation operations with validity status and errors
ValidationContext - Context type for validation operations with path and configuration

Branded Types

Branded<T, B> - Branded type with a specific brand identifier (supports string and unique symbol brands)
BrandSymbols - Predefined brand symbols for common use cases
BrandedWith<T, K> - Utility type to create branded types with predefined symbols
NonEmptyArray<T> - Array type that cannot be empty
NonEmptyString - String type that cannot be empty
PositiveNumber - Number type that must be positive
NegativeNumber - Number type that must be negative
NonNegativeNumber - Number type that must be non-negative
NonPositiveNumber - Number type that must be non-positive
PositiveInteger - Integer type that must be positive
NegativeInteger - Integer type that must be negative
NonNegativeInteger - Integer type that must be non-negative
NonPositiveInteger - Integer type that must be non-positive
Integer - Integer type
Nullable<T> - Type that can be null
Numeric - Numeric type (number or string that can be converted to number)
DateLike - Date-like type (Date object, date string, or numeric timestamp)
BooleanLike - Boolean-like type (boolean, "true"/"false", "1"/"0", or 1/0)
Pattern<P> - Branded string type that matches a specific regex pattern

🛠️ Error Generation

Guardz provides detailed error reporting with configurable error handling:

import { isType, isString, isNumber } from 'guardz';

const errors: string[] = [];
const config = {
  identifier: 'user',
  callbackOnError: (error: string) => errors.push(error),
  errorMode: 'multi', // 'single' | 'multi' | 'json'
};

const isUser = isType({
  name: isString,
  age: isNumber,
});

const invalidUser = { name: 123, age: 'thirty' };
const result = isUser(invalidUser, config);

console.log(errors);
// [
//   'user.name: Expected string, got number (123)',
//   'user.age: Expected number, got string ("thirty")'
// ]

Error Modes

single - Basic error messages (default)
multi - Detailed error messages with values
json - Hierarchical error tree structure

🎯 Utility Types

Guardz provides utility types for enhanced type safety:

import type { TypeGuardFn, TypeGuardFnConfig } from 'guardz';

// TypeGuardFn<T> - Type guard function type
// TypeGuardFnConfig - Configuration for type guards

🔐 Unique Symbol Branded Types

Guardz supports branded types with unique symbols for enhanced type safety:

import { isBranded, Branded, BrandSymbols, type BrandedWith } from 'guardz';

// Custom unique symbol brands
const UserIdBrand = Symbol('UserId');
type UserId = Branded<number, typeof UserIdBrand>;

const isUserId = isBranded<UserId>((value) => {
  return typeof value === 'number' && value > 0 && Number.isInteger(value);
});

// Predefined brand symbols
type Email = BrandedWith<string, 'Email'>;
const isEmail = isBranded<Email>((value) => {
  if (typeof value !== 'string') return false;
  const emailRegex = /^[^\s@]+@[^\s@]+\.[^\s@]+$/;
  return emailRegex.test(value);
});

// Usage
const id: unknown = 123;
if (isUserId(id)) {
  // id is now typed as UserId (number & { readonly brand: typeof UserIdBrand })
  console.log(id);
}

🤝 Contributing

We welcome contributions! Please see our Contributing Guide for details.

Development Setup

git clone https://github.com/thiennp/guardz.git
cd guardz
npm install
npm test

📄 License

This project is licensed under the MIT License - see the LICENSE file for details.

📚 Documentation

API Reference: GitHub README
Showcases: Complete TypeScript Examples - All possible TypeScript cases and real-world scenarios
Examples: Practical Usage Examples - Ready-to-run code samples
CHANGELOG: Version History - Latest updates and changes

🆘 Support

Issues: GitHub Issues
Discussions: GitHub Discussions
Email: nguyenphongthien@gmail.com

🔗 Related Projects

guardz-generator - Code generator for complex type guards and generic types
guardz-cli - Command-line interface for Guardz
guardz-vscode - VS Code extension for Guardz

🙏 Acknowledgments

Thanks to all contributors and the TypeScript community for making this project possible.

Made with ❤️ by the Guardz Team

Name		Name	Last commit message	Last commit date
Latest commit History 76 Commits
.github		.github
benchmarks		benchmarks
examples		examples
node_modules		node_modules
src		src
.eslintrc.js		.eslintrc.js
.gitignore		.gitignore
.prettierrc		.prettierrc
CHANGELOG.md		CHANGELOG.md
CODE_OF_CONDUCT.md		CODE_OF_CONDUCT.md
CONTRIBUTING.md		CONTRIBUTING.md
LICENSE		LICENSE
PERFORMANCE.md		PERFORMANCE.md
README.md		README.md
jest.config.js		jest.config.js
jest.setup.js		jest.setup.js
package-lock.json		package-lock.json
package.json		package.json
tsconfig.json		tsconfig.json

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Guardz

🚀 Quick Start

Installation

TypeScript Configuration

Basic Usage

🎯 Type Guards vs Validators

✨ Features

📖 Basic Examples

Basic Type Guards

isSymbol Example

Object Type Guards

Array Type Guards

Array Utilities

Union Types

Error Handling

Pattern Validation

🎯 Common Use Cases

API Response Validation

Form Data Validation

Database Result Validation

Configuration Validation

🔧 Advanced Features

Reusable Type Guard Patterns

Generic Types

Advanced Generic Patterns

Performance Optimizations

🔄 Migration Guide

From Zod

From Joi

From Yup

🛠️ Troubleshooting

Common Issues

TypeScript Errors

Performance Issues

Bundle Size Issues

Debugging

⚡ Performance Tips

Error Mode Selection

Validation Strategies

Caching Type Guards

🔧 API Reference

Primitive Type Guards

Special Type Guards

Array Type Guards

Object Type Guards

Number Type Guards

String Type Guards

Null/Undefined Type Guards

Union Type Guards

Web API Type Guards

Collection Type Guards

Utility Type Guards

Schema Type Guards

Advanced Type Guards

Type Guard Error Generation

Utility Types

Type Converters

Validation Types

Branded Types

🛠️ Error Generation

Error Modes

🎯 Utility Types

🔐 Unique Symbol Branded Types

🤝 Contributing

Development Setup

📄 License

📚 Documentation

🆘 Support

🔗 Related Projects

🙏 Acknowledgments

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