Modify method signature using decorators

[crisp cosmos]

Can I modify a method signature using stage 3 decorators? I have a method that receives 2 arguments

[steady matrix]

yeah, with stage 3 decorators in typescript, you can modify a method's behavior, but you cannot directly change the method's typescript signature at the type level

however, you can manipulate the arguments inside the decorator before passing them to the original method

for example, if you wanna modify the way arguments are passed to a method

function ModifyArgs() {
  return function (
    target: any,
    context: ClassMethodDecoratorContext
  ) {
    return function (this: any, ...args: any[]) {
      console.log('Original args:', args);
      
      // Modify arguments
      const newArgs = args.map(arg => String(arg).toUpperCase());

      return target.apply(this, newArgs);
    };
  };
}

class Example {
  @ModifyArgs()
  greet(name: string, message: string) {
    console.log(`Hello, ${name}: ${message}`);
  }
}

const e = new Example();
e.greet('John', 'welcome'); 
// Logs: "Hello, JOHN: WELCOME"

[crisp cosmos]

Thanks Dan! Hmmm so if I want to add parameters (For example, I wanna add a name + message param to the function) you'd suggest passing it inside some object as a "named parameter"?

[steady matrix]

yeah, exactly~~~

if you wanna add extra parameters dynamically, you'd typically wrap them in an object and mdify that inside the decorator

that way, you are not messing with the method signature directly but still achieving the flexibility you need

function AddParams(extraParams: Record<string, any>) {
  return function (target: any, context: ClassMethodDecoratorContext) {
    return function (this: any, ...args: any[]) {
      console.log('Original args:', args);

      // Inject extra parameters
      const modifiedArgs = [...args, extraParams];

      return target.apply(this, modifiedArgs);
    };
  };
}

class Example {
  @AddParams({ extra: 'Some additional info' })
  greet(name: string, message: string, extraParams?: Record<string, any>) {
    console.log(`Hello, ${name}: ${message}`);
    if (extraParams) {
      console.log('Extra params:', extraParams);
    }
  }
}

const e = new Example();
e.greet('John', 'welcome');
// Logs: "Hello, John: welcome"
// Logs: "Extra params: { extra: 'Some additional info' }"

you know, since typescript enforces method signatures at compile time, you cant directly modify them at runtime