AngularJS filter with cached data got from a service using promise API

promise-filter.angular.js

app.filter("testf", function($timeout) {
    var data = null; // DATA RECEIVED ASYNCHRONOUSLY AND CACHED HERE
    var invoked = false
    function realFilter(value) { // REAL FILTER LOGIC
        return ...;
    }

    return function(value) { // FILTER WRAPPER TO COPE WITH ASYNCHRONICITY
        if( data === null ) {
            if (!invoked){
                invoked = true;
                // IF IT HAS NOT BEEN CALLEd YET, CALL THE SERVICE THAT FETCHES THE DATA HERE
                callService.then(function(result) {
                    data = result;
                });    
            }
            
            return "-"; // PLACEHOLDER WHILE LOADING, COULD BE EMPTY
        }
        else return realFilter(value);
    }
});