Angular2 - How to chain async http requests and stop if fails

I have an array of HTTP requests that I need to fire in certain order, but if any of the previous one fails then none of the following ones is going to be executed.

1. How can I achieve that?

2. What's the best approach?

I need something like:

  let failed: boolean = false;
  payloadArray.forEach(payload => {
     if (!failed) {
     http.post(this.url, payload, this.options)
     .map((res: Response) => {
        return res.json;
      })
    .catch((error: any) => {
          failed = true;
          Observable.throw(error.json().error || 'Server error')
       });
     }
  }