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Looking at this AuthInterceptor from this helpful answer, how are the request and response key's used in the returned JSON object?

Also, what's the meaning of return config || $q.when(config)? I understand that the second part is returned if config is null or undefined, but what does $q.when(config) mean in this code?

myApp.factory('AuthInterceptor', function ($window, $q) {
    return {
        'request': function(config) {
            config.headers = config.headers || {};
            if ($window.sessionStorage.getItem('token')) {
                config.headers.Authorization = $window.sessionStorage.getItem('token');
            }
            return config || $q.when(config);
        },
        'response': function(response) {
            if(response.status === 401) {
                $location('/login');
            }
            return response || $q.when(response);
        }
    };
});

I typed out the above linked answer. It worked for me, but I don't understand how it's used.

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2 Answers 2

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When registering an $http interceptor, you should essentially pass an object with the following (optional) keys: request, requestError, response, responseError.
For more info on when each interceptor function is called, take a look at this answer.

$q.when() turns any JS object into a promise (that resolved immediatelly with the passed in object as each resolved value). But, frankly (although I've seen it a lot) I don't understand why one would need to return config || $q.when(config), instead of just config.

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2 Comments

could you please say a bit more: I don't understand why one would need to return config || $q.when(config), instead of just config.? I'd like to know what you're thinking, please.
Actually, there nothing moe to say other than what I said in my comment to Matt Way's answer (which is essentially what you said in your comment).
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request and response are simple used as intermediaries. In other words, the request function is run prior to a request (after requesting), and the response function is run prior to handling a request result.

$q.when() ensures that the return value is able to be handled as a promise. Essentially it wraps the value in a promise, so that functions like returnedValue.then() work.

See: https://docs.angularjs.org/api/ng/service/$q

Kevin asked why you would want to use $q.when(). This is to ensure that any outside function that consumes this one receives a promise, if it is expecting one. For example, imagine the situation where you call a function expecting a promise:

someThirdPartyFunc(someArg).then(function(result){
    // do somethign with result
});

If you ran this and someThirdPartyFunc returned a simple value (say 100), then this would obviously fail. If the implementor wrapped the return value in $q.when(100), then the function call above would be valid, and result would contain the value 100.

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why would you want to handle a return variable as a promise?
Updated answer for you.
so let's say that my regular, non-intercepting code executes: $http.post("foo/bar.com"), expecting a promise back. This HTTP POST returns an object: {count: 100}. The above response property of my AuthInterceptor would return the object as response is truthy. Wouldn't this implementation then break the expected promise result of the caller of the $http.post(...)? Or perhaps it's up to the implementor to decide whether to return response or response wrapped in a promise?
This is why I don't see the purpose of returning a promise. Normally (i.e. if config is defined) the function will return an object (not a promise), but if config is not defined then it will return a promise (wrapped around the undefined config). It doesn't make sense and indeed it seems like breaking your own implementation (but again I might be missing something).

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