Modern Decorators

Goal

Create a standard TypeScript method decorator that validates its application target and contributes to class metadata without accessing the class constructor.

Implementation

import {
    Methods,
    getMetadataContainer,
} from '@litert/decorator';

function route(path: string): Methods.ICallbackFn {

    return Methods.withArgsCheck((_method, ctx) => {
        ctx.metadata!['route:' + String(ctx.name)] = path;
    });
}

class Controller {

    @route('/users')
    public listUsers(): void {}
}

const metadata = getMetadataContainer(Controller);
console.log(metadata.get('route:listUsers'));

Example code

Decorator kind	Example
Class	Class.ts
Method	Method.ts
Property	Property.ts
Accessor	Accessor.ts
Getter	Getter.ts
Setter	Setter.ts
Static method	StaticMethod.ts
Static property	StaticProperty.ts
Static accessor	StaticAccessor.ts
Static getter	StaticGetter.ts
Static setter	StaticSetter.ts

Notes

Step	Reason
Use Methods.withArgsCheck	The generated decorator throws when applied to the wrong kind of element.
Write to ctx.metadata	Modern member decorators do not receive the owning class constructor or prototype. The metadata object is the shared class configuration container.
Read through getMetadataContainer	Application code can read the completed class metadata after the class has been defined.

For larger decorators, prefer a single metadata key that stores a structured class configuration object. Let class, instance member, and static member decorators add their own entries to that object, then read the final result from getMetadataContainer(YourClass).