Example of decorated interfaces...

decorated-queries.ts

interface Query {
	query(sql: string): Promise<any>
}

class QueryImplementation implements Query {
	query(sql: string) {
		return new Promise<string>(resolve => {
			setTimeout(() => resolve('Hello'), 2000)
		})
	}
}

class QueryCachedDecorator implements Query {
	constructor(private readonly inner: Query) {}

	private cache: { [query: string]: any } = {}

	async query(sql: string): Promise<any> {
		let result = this.cache[sql]
		if (result === undefined) {
			result = this.cache[sql] = await this.inner.query(sql)
		}
		return result
	}
}

class QueryDiagonsticsDecoractor implements Query {
	constructor(private readonly inner: Query, private readonly label: string) {}

	async query(sql: string): Promise<any> {
		const label = `${this.label}: ${sql}`
		console.time(label)
		try {
			return await this.inner.query(sql)
		} finally {
			console.timeEnd(label)
		}
	}
}

const q: Query = new QueryDiagonsticsDecoractor(
	new QueryCachedDecorator(new QueryImplementation()),
	'outer diagnostics'
)

async function run() {
	q.query('select * from hello')
	q.query('select * from hello')
	q.query('select * from hello')
}

run()