angular1-async-filter/async-filter.js

Angular2 async pipe implemented as Angular 1 filter to handle promises & RxJS observables

'use strict';

(function (angular) {
    function asyncFilter() {
        var values = {};
        var subscriptions = {};

        function async(input, scope) {
            // Make sure we have an Observable or a Promise
            if (!input || !(input.subscribe || input.then)) {
                return input;
            }

            var inputId = objectId(input);
            if (!(inputId in subscriptions)) {
                var subscriptionStrategy = input.subscribe && input.subscribe.bind(input) || input.success && input.success.bind(input) // To make it work with HttpPromise
                 || input.then.bind(input);

                subscriptions[inputId] = subscriptionStrategy(function (value) {
                    values[inputId] = value;

                    if (scope && scope.$applyAsync) {
                        scope.$applyAsync(); // Automatic safe apply, if scope provided
                    }
                });

                if (scope && scope.$on) {
                    // Clean up subscription and its last value when the scope is destroyed.
                    scope.$on('$destroy', function () {
                        var sub = subscriptions[inputId];
                        if (sub) {
                            sub.unsubscribe && sub.unsubscribe();
                            sub.dispose && sub.dispose();
                        }
                        delete subscriptions[inputId];
                        delete values[inputId];
                    });
                }
            }

            return values[inputId];
        };

        // Need a way to tell the input objects apart from each other (so we only subscribe to them once)
        var nextObjectID = 0;
        function objectId(obj) {
            if (!obj.hasOwnProperty('__asyncFilterObjectID__')) {
                obj.__asyncFilterObjectID__ = ++nextObjectID;
            }

            return obj.__asyncFilterObjectID__;
        }

        // So that Angular does not cache the return value
        async.$stateful = true;

        return async;
    };

    angular.module('asyncFilter', []).filter('async', asyncFilter);
})(angular);