"Computed Properties" in AngularJS -

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i chose angularjs on ember.js project working on, , have been pleased far. 1 nice thing ember built in support "computed properties" automatic data binding. have been able accomplish similar in angular code below, not sure if best way so.

// controller angular.module('mathskills.controller', [])   .controller('nav', ['navigation', '$scope', function (navigation, $scope) {     // "computed property"     $scope.$watch(navigation.getcurrentpagenumber, function(newval, oldval, scope) {       scope.currentpagenumber = newval;     });     $scope.totalpages = navigation.gettotalpages();   }]);  // 'navigation' service angular.module('mathskills.services', [])   .factory('navigation', function() {     var currentpage = 0,         pages = [];      return {       getcurrentpagenumber: function() {         return currentpage + 1;       },       gettotalpages: function() {         return pages.length;       }     };   });  // html template <div id=problempager ng-controller=nav>   problem {{currentpagenumber}} of {{totalpages}} </div>

i ui update whenever currentpage of navigation service changes, above code accomplishes.

is best way solve problem in angularjs? there (significant) performance implications using $watch() this? better accomplished using custom events , $emit() or $broadcast()?

while self-answer works, doesn't implement computed properties. solved problem calling function in binding force binding greedy. i'm not 100% sure it'd work in cases, , greediness might have unwanted performance characteristics in situations.

i worked solution computed properties w/dependencies similar emberjs has:

function ngcreatecomputedproperty($scope, computedpropertyname, dependentproperties, f) {   function assignf($scope) {     var computedval = f($scope);     $scope[computedpropertyname] = computedval;   };    $scope.$watchcollection(dependentproperties, function(newval, oldval, $scope) {     assignf($scope);   });   assignf($scope); };  // in controller... ngcreatecomputedproperty($scope, 'asquared', 'a',     function($scope) { return $scope.a * $scope.a } ); ngcreatecomputedproperty($scope, 'aplusb',   '[a,b]', function($scope) { return $scope.a + $scope.b } );

see live: http://jsfiddle.net/apinstein/2kr2c/3/

it's worth noting $scope.$watchcollection efficient -- verified "assignf()" called once if multiple dependencies changed simultaneously (same $apply cycle). "


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