What are parameter decorators in TypeScript?

Can you explain what parameter decorators are in TypeScript?

Sure! Parameter decorators are a special kind of decorator in TypeScript that can be applied to the parameters of a method. They allow you to modify or observe the behavior of the parameter.

How do you define a parameter decorator?

You define a parameter decorator as a function that takes three arguments: the target object, the name of the method, and the index of the parameter. It can be used to add metadata or modify the parameter.

Can you give me an example of a parameter decorator?

Absolutely! Here's a simple example:

function Log(target: any, methodName: string, paramIndex: number) {
    console.log(`Parameter at index ${paramIndex} in method ${methodName} was decorated.`);
}

class Example {
    greet(@Log message: string) {
        console.log(message);
    }
}

In this example, the Log decorator logs the index of the parameter whenever the greet method is called.

What are some use cases for parameter decorators?

Parameter decorators can be used for various purposes, such as logging, validation, or injecting dependencies in frameworks like Angular.