Javascript Cognito了解异步并等待？

Question

I'm calling this function to retrieve a user attribute, however when i'm testing the function the return result is always "test" and then it goes through "cognitoUser.getUserAttributes" and logs the actual result. I'm not sure why but "cognitoUser.getUserAttributes" seems to be skipped initially.

when run, it prints out test and instead of the actual result

any ideas?

function retrieveattribute(e) {
  var ans = "test";
  var e = "custom:InstanceID_1";
  cognitoUser.getUserAttributes(function(err, result) {
    if (err) {
      alert(err);
      return;
    }
    for (i = 0; i < result.length; i++) {
      if (result[i].getName() == e) {
        ans = result[i].getValue();
        console.log(ans);
        return ans;
      }
    }
  });
  return ans;
}

Answer 1

For start "async code" you need wrap you function to promise:

function retrieveattribute(e) {
    return new Promise(function(res) {
        var ans = "test";
        var e = "custom:InstanceID_1";

        cognitoUser.getUserAttributes(function(err, result) {
            if (err) {
                alert(err);
                return;
            }
            for (i = 0; i < result.length; i++) {
                if (result[i].getName() == e) {
                    ans = result[i].getValue();
                    console.log(ans);
                    res(ans);
                }
            }
        });
    })
}

After it you can use as promise:

   retrieveattribute(e).then(t => console.log(t))

Or await it at async function:

   await retrieveattribute(e)