Angular Performance 101

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Disclaimer

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“Premature optimization is the root of all Evil”

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A story

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Why did it keep updating?

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$interval(function() {  $http.get(‘/events’) .success(function(events) { if (events) { $scope.events = events; } }); }, 20 * 1000);

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Why?

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Angular == SO. MUCH. MAGIC.

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“With great power comes great responsibility”

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We’ll learn How dirty checking is performed When it runs What you should do

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The Secret

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Magic == Dirty checking

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How dirty checking is performed

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Digest Loop

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Digest == Run all watch expressions

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$scope.$watch()

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… and {{ stuff }}

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… and ng-show=“foo()”

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… and isolated scope variables scope: {foo: ‘=’}

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… and {{ value | myFilter }}

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… and ng-repeat itself

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Watch Expressions $scope.$watch() {{ stuff }} ng-show=“list.length > 0” isolated scope bindings: {foo: ‘=’} ﬁlters: {{ date | fromNow }} ng-repeat Basically everything

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When does it run?

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User actions

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ng-click

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ng-change

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ng-model

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… and $http responses

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… and when $q promises are resolved

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… and when using $timeout or $interval

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… and whenever you call $scope.$apply() or $scope.$digest()

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When digest runs User actions (ng-click, ng-model, etc.) $http responses $q promises resolved $timeout / $interval $scope.$apply() / $scope.$digest() Basically: a lot of things

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So? Who cares?

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But when the shit hits the fan

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You click and the screen freezes for a while The only* performance issue that is angular’s fault

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Are all clicks slow? Or just a certain screen?

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One Screen is Slow That screen has bad scopes: Too many watches Watch handlers that take too long

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Everything is Slow Your digest loop is taking too long You’re doing it wrong

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Pinpoint it

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Batarang

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See watch expression

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See slow expressions

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Time Your $digest console.time(‘digest’); $rootScope.$digest(); console.timeEnd(‘digest’); http://jsﬁddle.net/mbRf8/

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What you should do

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Make watches faster

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Making Watches Faster Switch deep watch with $watchCollection $scope.$watch(‘myList’, function() {}, true); ! $scope.$watchCollection(‘myList’, function() {});

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Making Watches Faster Deep watch a subset $scope.$watch(‘myList’, function() {}, true); ! $scope.$watch( function() {return _.pluck($scope.myList, ‘id’);}, function() {}, true);

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Making Watches Faster Make the change handler more performant

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Have less watches

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ng-repeat is your enemy

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ng-repeat is your enemy Use track by

http://bit.ly/1kyvet7

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ng-repeat is your enemy Paginate

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ng-repeat is your enemy Row Virtualization à-la ng-grid http://angular-ui.github.io/ng-grid/

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ng-repeat is your enemy Bind Once https://github.com/Pasvaz/bindonce

! !

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Have Less Watches ng-hide & ng-show elements are still there, consider using ng-if Consider replacing ﬁlters with  pre-calculated values

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Badass AKA “I’m Desperate”

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Badass Mode Write an angular-less widget

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Your Mission Pinpoint bad watches Make watches faster Use less watches

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Thank You! Aviv Ben-Yosef @avivby www.deﬂect.io ! My angular & web development newsletter www.codelord.net