Toy example of a messages interface for typescript

message-interface.ts

interface IMessage<TKey extends string, TPayload> {
	key: TKey;
	payload: TPayload;
}

type GenericMessage = IMessage<string, any>;

module foo {
	type FooBarKeyT = "foo.bar";
	const FooBarKey: FooBarKeyT = "foo.bar";
	type FooQuuxKeyT = "foo.quux";
	const FooQuuxKey: FooQuuxKeyT = "foo.quux";
	
	export type FooBar = IMessage<FooBarKeyT, {v: number}>;
	export type FooQuux = IMessage<FooQuuxKeyT, {v: string}>;
	export type FooMessage = FooBar | FooQuux;
	
	export function isFooMessage(m:GenericMessage): m is FooMessage {
		return m.key === FooBarKey || m.key === FooQuuxKey;
	}
	
	export function isFooBarMessage(m:FooMessage): m is FooBar {
		return m.key === FooBarKey;
	}
	
	export function isFooQuuxMessage(m:FooMessage): m is FooQuux {
		return m.key === FooQuuxKey;
	}

	
	export function fooBarMessage(v: number): FooMessage {
		return {key: FooBarKey, payload: {v: v}};
	}
	
	export function fooQuuxMessage(v: string): FooMessage {
		return {key: FooQuuxKey, payload: {v: v}};
	}
}


module consumer {
	const m:GenericMessage = foo.fooBarMessage(23);
	
	if (foo.isFooMessage(m)) {
		if (foo.isFooBarMessage(m)) {
			console.log(Math.pow(2, m.payload.v));
		}	
		else if (foo.isFooQuuxMessage(m)) {
			console.log(m.payload.v.toUpperCase());
		}	
	}	
}