In the post Asynchronous Programming with Async and Await, I compaired asyncchronous programming in C#, ES7(ES2016) and TypeScript. It surprises me that TypeScript has already implemented async and await and has a fully support. Here I’m going to talk a little bit more about how to use Template with Promise so as to support return type of await result.

For example, here’s last snippet:

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async function delay(ms: number) {
  return new Promise(resolve => setTimeout(resolve, ms));
}

async function ping(someone) {
  for (var i = 0; i < 5; i++) {
    await delay(1000);
    console.log("ping " + someone);
  }
}

ping('zp_j');

How to support return value with defined type for the method deplay()? Here’s the solution:

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function delay(ms: number) {
  return new Promise<number[]>(
    resolve => setTimeout(
      () => resolve([0, 1, 2]), ms
    )
  );
}

async function ping(someone: string) {
  for (var i = 0; i < 5; i++) {
    let result: number[] = await delay(1000);
    console.log("ping " + someone + " with return value: " + JSON.stringify(result));
  }
}

ping('zp_j');

Here we add the return type to Promise, because Promise use a template as the return type. When we call delay() the return type is set to be number[].