Allow decorators (and metadata) on non-class functions

[Roaders]

Search Terms

function decorators

Suggestion

Decorators and the metadata that they produce are great. As far as I can see this is only supported on classes, class properties and class functions.
I would like to be able to decorate anything. Specifically I would like to decorate a function that is not defined in a class so that at runtime I can get metadata about the types of parameters it expects.

Use Cases

Class metadata can be used by DI systems to inject constructor params. I would like to write code that does the same for a function. Specifically I would like to write a DI system for a React Function component to resolve any parameters (or dependencies) that function has.

Examples

@storeMetadata()
function myReactFuntion(params: IParams, service: SomeService, util: SomeUtil){
    return someReactInstance();
}

function performInjectMagic(func: (...args: any[]) => any){
    return (params: IParams) => {
         const diArgs = evaluateAndInstantiateBasedOnMetaData(func);

         return func(params, ...diArgs);
   }
}

export const performInjectMagic(myReactFunction);

Checklist

My suggestion meets these guidelines:

• This wouldn't be a breaking change in existing TypeScript/JavaScript code
• This wouldn't change the runtime behavior of existing JavaScript code
• This could be implemented without emitting different JS based on the types of the expressions
• This isn't a runtime feature (e.g. library functionality, non-ECMAScript syntax with JavaScript output, etc.)
• This feature would agree with the rest of TypeScript's Design Goals.

[MartinJohns]

Duplicate of #7318. And this would first require JavaScript to support function decorators.