What are TypeScript decorators and how do I use them?

What are TypeScript decorators and how do I use them?

TypeScript decorators are special annotations that can be attached to classes, methods, or properties to modify their behavior. They are a powerful feature that allows for metaprogramming.

Can you give me an example of a class decorator?

Sure! Here's a simple example of a class decorator:

function LogClass(target: Function) {
    console.log(`Class ${target.name} is created.`);
}

@LogClass
class MyClass {
    constructor() {
        console.log('MyClass instance created.');
    }
}

This decorator logs a message when the class is created.

What about method decorators? How do they work?

Method decorators can be used to modify the behavior of a method. Here's an example:

function LogMethod(target: any, propertyName: string, descriptor: PropertyDescriptor) {
    const originalMethod = descriptor.value;
    descriptor.value = function(...args: any[]) {
        console.log(`Calling ${propertyName} with arguments: ${args}`);
        return originalMethod.apply(this, args);
    };
}

class MyClass {
    @LogMethod
    myMethod(arg: string) {
        console.log(`Argument: ${arg}`);
    }
}

This decorator logs the arguments passed to the method.

Are there any limitations or caveats I should be aware of?

Yes, decorators are an experimental feature in TypeScript, so they may change in future versions. Additionally, they can make your code harder to understand if overused, so it's best to use them judiciously.