typeChecker

A lightweight, flexible and template-based type checker for JavaScript. Enforce strong type safety on functions and classes without TypeScript.

📦 NPM 包名：@dongxiang678/typechecker
安装：npm install @dongxiang678/typechecker --save

Features

• ✅ Template-based type constraint (support all JS types: Number/String/Array/Custom Class)
• ✅ Strong type checking for function parameters & return values
• ✅ No implicit type conversion between different types
• ✅ Lightweight (0 dependencies), easy to integrate
• ✅ Compliant with JavaScript ecosystem norms (suitable for large projects)

Installation

npm install @dongxiang678/typechecker --save
# or yarn
yarn add @dongxiang678/typechecker

Quick Start

1. Basic Type Check

const { createCheckerTemplate, enforceReturnType } = require('@dongxiang678/typechecker');

// Create a checker template for String type
const StringChecker = createCheckerTemplate(String);

// Enforce function to return StringChecker
const getString = enforceReturnType(StringChecker, (value) => {
  const checker = new StringChecker();
  return checker.check(value);
});

// Success
console.log(getString("Hello typeChecker!").getValue()); // "Hello typeChecker!"

// Error: Number type cannot be converted to String
try {
  getString(123);
} catch (err) {
  console.error(err.message); // "Return value type error: Checker<Number> cannot be converted to Checker<String>"
}

2. Custom Class Check

const { createCheckerTemplate, enforceFunctionType } = require('typeChecker');

class User {
  constructor(name) {
    this.name = name;
  }
}

// Create a checker template for User class
const UserChecker = createCheckerTemplate(User);

// Enforce parameter & return type (UserChecker)
const getUser = enforceFunctionType([UserChecker], UserChecker, (checker) => {
  return checker.check(new User("张三"));
});

// Success
const userChecker = new UserChecker(new User("李四"));
console.log(getUser(userChecker).getValue().name); // "张三"

API

createCheckerTemplate(targetType)

Create a type checker template for specific type.

• targetType: Function (e.g., String, User) or string (e.g., "Number")
• Returns: Checker class with type constraint

enforceFunctionType(paramCheckers, returnChecker, fn)

Enforce type checking for function parameters and return value.

enforceReturnType(returnChecker, fn)

Simplified: only enforce return value type.

Why Choose This?

• Solve type-related bugs in pure JavaScript projects
• No TypeScript required, but achieve strong type safety
• Lightweight and modular (works with any project scale)
• Intuitive API, easy to learn and use

License

MIT