Angular2同步承诺

Question

In Ionic 2 the get function for accessing localStorage returns a promise. The problem with the below code is that the headers object gets returned before it has been appended with the Authorization key. How could I modify the below function such that the headers object is returned only after the promise is resolved.

private _createAuthHeaders(): Headers {
    let headers = new Headers({
        'Accept': 'application/json',
        'Content-Type': 'application/json'
    });
    this.local.get('authToken').then(res=>{
      headers.append('Authorization', res);
    }, err=>{
      headers.append('Authorization', '');
    });
    return headers;
}

Answer 1

I would refactor your code this way:

private _createAuthHeaders(): Headers {
  let headers = new Headers({
    'Accept': 'application/json',
    'Content-Type': 'application/json'
  });
  this.local.get('authToken').then(res=>{
    headers.append('Authorization', res);
    return headers;
  }, err=>{
    headers.append('Authorization', '');
    return headers;
  });
}

and you can use this method like this:

this._createAuthHeaders().then(headers => {
  // do something like setting the headers on the request
  // and execute it...
});

Edit

You can leverage promise chaining to make your code cleaner. Here is a sample:

this._createAuthHeaders().then(headers => {
  // do something like setting the headers on the request
  // and execute it...
  return this.http.get('some url', { headers: headers }).toPromise();
}).then(result => {
  // handle result
});