How to get function parameter names/values dynamically?

Question

Is there a way to get the function parameter names of a function dynamically?

Let’s say my function looks like this:

function doSomething(param1, par         


        

Answer 1

As this has not yet been mentioned, if you are using Typescript you can emit meta-data when using Decorators which will allow you to get the parameter names and types.

Metadata will only be emitted if the class/function/prop has a decorator on it.
It doesn't matter which decorator.

This feature can be enabled by setting emitDecoratorMetadata to true inside tsconfig.json

{
  "compilerOptions": {
    "emitDecoratorMetadata": true
  }
}

As the metadata is still an early proposal the reflect-metadata package must be installed or Reflect.getMetadata will not be defined.

npm install reflect-metadata

You can use it as follows:

const AnyDecorator = () : MethodDecorator => {
    return target => { }
}

class Person{
    @AnyDecorator()
    sayHello(other: Person){}
}
const instance = new Person();
const funcType = Reflect.getMetadata('design:type', instance.sayHello);
const funcParams = Reflect.getMetadata('design:paramtypes', instance.sayHello);

In newer versions of Angular for instance this is used to determine what to inject -> https://stackoverflow.com/a/53041387/1087372