TypeScript Decorators Example

This project demonstrates the use of decorators in TypeScript to modify and enhance class behavior.

Features

• Class Decorator: SimpleLogger logs the instantiation of a class.
• Method Decorator: LogMethod logs method calls and their arguments.
• Accessor Decorator: MyReadOnly makes a property read-only.

Setup and Installation

1. Clone the repository:

git clone <https://github.com/el-riber/mob3>
cd typescript-decorators

2. Install dependencies:

npm install

3. Build the project:

npm run build

4. Run the project:

npm start

Project Structure

• src: Contains the source TypeScript files.
  • MyTestClass.ts: Contains the MyTestClass class with applied decorators.
  • decorators.ts: Contains the SimpleLogger, LogMethod, and MyReadOnly decorators.
  • index.ts: Entry point for testing the decorators.
• dist: Contains the compiled JavaScript files.
• tsconfig.json: TypeScript configuration file.
• package.json: Project configuration and dependencies.

Example Usage

Class Decorator

Logs when an instance of MyTestClass is created:

@SimpleLogger
class MyTestClass {
  // class implementation
}

Method Decorator

Logs method calls and arguments:

@LogMethod
method1(): void {
  console.log(`Method1 called: prop1 = ${this.prop1}`);
}

Accessor Decorator

Prevents modification of a property:

@MyReadOnly
get prop3(): string {
  return this._prop3;
}

Testing Decorators

In the src/index.ts file, we test the decorators by creating instances and calling methods/accessors.

import MyTestClass from './MyTestClass';

const instance = new MyTestClass('test', 42);
instance.method1();
instance.method2();

console.log(`Property prop3: ${instance.prop3}`);
try {
  (instance as any).prop3 = 'new value';  // This should throw an error
} catch (e) {
  if (e instanceof Error) {
    console.error('Error:', e.message);  // This should log the error message
  } else {
    console.error('An unknown error occurred');
  }
}

const anotherInstance = new MyTestClass('anotherTest', 99);
anotherInstance.method1();
anotherInstance.method2();

console.log(`Property prop3: ${anotherInstance.prop3}`);

Expected Output

You should see logs similar to:

SimpleLogger: Creating instance of MyTestClass
Calling method1:
LogMethod: Calling method1 with []
Method1 called: prop1 = test
Calling method2:
LogMethod: Calling method2 with []
Method2 called: prop2 = 42
Accessing prop3:
default
Trying to modify prop3:
Error: Cannot set property prop3
Creating a new instance of MyTestClass:
SimpleLogger: Creating instance of MyTestClass
Calling method1 on anotherInstance:
LogMethod: Calling method1 with []
Method1 called: prop1 = anotherTest
Calling method2 on anotherInstance:
LogMethod: Calling method2 with []
Method2 called: prop2 = 99
Accessing prop3 on anotherInstance:
default

This output confirms that the decorators are working as expected, logging method calls, preventing property modification, and logging class instantiation.

License

This project is licensed under the ISC License.