$q: check if promise is resolved

[richard-uk1]

I think it's probably easiest to describe the use case:

When the user clicks a button, a GET request for some resource is sent to the server.

• The user clicks the button
• The user clicks the button again before the AJAX request has returned

I don't want to issue 2 requests for the same data, so I return the original promise to the second request. For example:

factory('DataService', ['$http', '$q', function($http, $q) {
    var load_data = false;
    return {
        /**
         * This function is unchanged when called multiple times - so it is
         * safe to just return the same promise as for a prev call
         */
        load: function(id) {
            if(load_data) return load_data.promise;
            load_data = $http({
                method: 'GET',
                url: '/some/resource/'+id,
            });
            return load_data.promise;
        }
    };  
}]);

The above code won't work in the case where the promise has returned, I see the ideal solution as the ability to do this:

factory('DataService', ['$http', '$q', function($http, $q) {
    var load_data = false;
    return {
        /**
         * This function is unchanged when called multiple times - so it is
         * safe to just return the same promise as for a prev call
         */
        load: function(id) {
            if(load_data && !load_data.resolved) return load_data.promise;
            load_data = $http({
                method: 'GET',
                url: '/some/resource/'+id,
            });
            return load_data.promise;
        }
    };  
}]);

The stack overflow question here: http://stackoverflow.com/questions/17885979/how-to-check-whether-an-angular-q-promise-is-resolved discusses the situation.

What are your thoughts on this? (Apologies if this is a duplicate - I did look and couldn't find anything)

[jeffbcross]

I don't think we want to extend the $q implementation beyond what is required of A+, or what is provided by the ES6 spec. The right way to handle your use case is to cache the data in the service, and in load() you can see if data is loaded and return it as $q.when(data), which casts the value as a promise. And if load is request is already pending, return the existing load_data.promise.