JavaScript的麻烦理解Windows 8的承诺

Question

So I am writing a quick app that involves some oauth2 is what the end result to be is a method which is in charge of the oauth access token flow so it will do the following:

1. check if we have a token if we don't get an access token
2. check if the token is expired if not we should refresh it
3. otherwise return the token

the pesudo code for this generally looks like this:

if token == null
   token = getAccessToken() //I am going block the app until I get my token kthxbi

if expired(token)
   token = refreshAcessToken() //I am going block the app until I refresh my token kthxbi

return token

this way when I call this method I know I am always being returned a valid token. The problem I am running into is that to get an access token or to refresh it we need to use a promise. The code for that normally looks like this:

getAccessToken() {
    return WinJS.xhr({ type: "post", url: "i am a url rawr", 
                     responseType: "json", data: data}).done(

                     function do stuff(){});
}

I get that I can't just return the access code that I get in the function do stuff as its asynchronous (I can however return that promise). This leads my problem. I do not want to have to wrap every request I do in some sort of asychnronus statement! I need the access token to do anything else in the app however I cannot get a definite value from the access token untill the promise has been created. (Surley this would mean that I would need to wrap every function that calls this function in a .then() or .done() statement).

can someone shed some light on this. My perdicument is that my handleOAuth now looks like this

this.getToken = function() {
    if (token === null) {

        //test is a function that makes a xhr request to the server
        test().done(
              function complete(result) {
                  token = JSON.parse(result.responseText);
                  lastTokenTime = getTokenExpiry(token['expiry']);
              },
              function error(error) {
                  console.log(JSON.stringify(serializedData));
                  console.log(error.innerText);
              }
        );

       //refresh

     return token; #I am going return null as the promise is not done yet
    }

which is obvoius not great as I can't just return the value of token as its dependent on the promise from test() to get the token value. Idealy I'd like for some way of saying don't return the token until we have a value but this breaks the entire purpose of asychronous statements!. What should I do in this situation.

Answer 1

 return token; #I am going return null as the promise is not done yet

No, you should return the promise itself. That's how promises are meant to work. You return the promise, and then code consuming yours can bind additional callbacks to the promise's done/fail callbacks.

Answer 2

It looks like you can change from using WinJS to using a standard XMLHttpRequest. Then you can make it synchronous and not need to use a promise. This will bring you back into the synchronous paradigm.

http://social.msdn.microsoft.com/Forums/windowsapps/en-US/b261daa9-5101-4538-989d-435e1681d64c/synchronous-winjsxhr-request?forum=winappswithhtml5

You might look into how better to fit into the asynchronous model as it will provide a better user experience.