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twitter.com/mgechev github.com/mgechev blog.mgechev.com Faster Applications Minko Gechev

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twitter.com/mgechev github.com/mgechev

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Runtime Performance

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twitter.com/mgechev Simplified Business application

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AppComponent EmployeesListComponent

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AppComponent EmployeesListComponent

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AppComponent EmployeesListComponent

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{{ item.label }} {{ calculate(item.num) }} #

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{{ item.label }} {{ calculate(item.num) }} #

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{{ item.label }} {{ calculate(item.num) }} #

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{{ item.label }} {{ calculate(item.num) }} #

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@Component(##...) export class EmployeeListComponent { @Input() data: EmployeeData[]; @Output() remove = new EventEmitter(); @Output() add = new EventEmitter(); handleKey(event: any) { ##... } calculate(num: number) { return fibonacci(num); } }

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@Component(##...) export class EmployeeListComponent { @Input() data: EmployeeData[]; @Output() remove = new EventEmitter(); @Output() add = new EventEmitter(); handleKey(event: any) { ##... } calculate(num: number) { return fibonacci(num); } }

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AppComponent EmployeesListComponent data

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@Component(##...) export class EmployeeListComponent { @Input() data: EmployeeData[]; @Output() remove = new EventEmitter(); @Output() add = new EventEmitter(); handleKey(event: any) { ##... } calculate(num: number) { return fibonacci(num); } }

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const fibonacci = n #=> { if (n ##=== 1 #|| n ##=== 2) return 1; return fibonacci(n - 1) + fibonacci(n - 2); };

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f(n) f(n-1) f(n-2) f(n-3) f(n-4) f(n-2) f(n-3) ...

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f(n) f(n-1) f(n-2) f(n-3) f(n-4) f(n-2) f(n-3) ...

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f(n) f(n-1) f(n-2) f(n-3) f(n-4) f(n-2) f(n-3) ...

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Slowing it down artificially

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twitter.com/mgechev Application Structure • An application component • Two list components • Slow computation for each entry

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twitter.com/mgechev Real data…

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140 entries

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Why that slow?

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@Component(##...) export class EmployeeListComponent { ##... calculate(num: number) { console.log('Computing for entry in', this.department); return fibonacci(num); } }

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AppComponent EmployeeListComponenet (sales) EmployeeListComponenet (r&d) E1 E2 En … E1 E2 En … Ignored details for simplicity

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AppComponent EmployeeListComponenet (sales) EmployeeListComponenet (r&d) E1 E2 En … E1 E2 En … Ignored details for simplicity

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AppComponent EmployeeListComponenet (sales) EmployeeListComponenet (r&d) E1 E2 En … E1 E2 En … Ignored details for simplicity

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AppComponent EmployeeListComponenet (sales) EmployeeListComponenet (r&d) E1 E2 En … E1 E2 En … Ignored details for simplicity

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AppComponent EmployeeListComponenet (sales) EmployeeListComponenet (r&d) E1 E2 En … E1 E2 En … Ignored details for simplicity

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AppComponent EmployeeListComponenet (sales) EmployeeListComponenet (r&d) E1 E2 En … E1 E2 En … Ignored details for simplicity

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AppComponent EmployeeListComponenet (sales) EmployeeListComponenet (r&d) E1 E2 En … E1 E2 En … Ignored details for simplicity

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AppComponent EmployeeListComponenet (sales) EmployeeListComponenet (r&d) E1 E2 En … E1 E2 En … Ignored details for simplicity

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twitter.com/mgechev Ideas for optimization?

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twitter.com/mgechev OnPush Change Detection Strategy

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twitter.com/mgechev With OnPush change detection will be triggered when the framework, with reference check, determines that any of the inputs of a component has changed…

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twitter.com/mgechev Lets think of EmployeeListComponent as a function, where: What does this mean? • Inputs are function’s arguments • Rendered component is function’s result

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Pseudo code (not Angular) const f = EmployeeListComponent; const data = [e1]; #// Will trigger CD f({ data: data }); data.push(e2); #// Will not trigger CD f({ data: data }); #// Will trigger CD f({ data: data.slice() });

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Pseudo code (not Angular) const f = EmployeeListComponent; const data = [e1]; #// Will trigger CD f({ data: data }); data.push(e2); #// Will not trigger CD f({ data: data }); #// Will trigger CD f({ data: data.slice() });

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Pseudo code (not Angular) const f = EmployeeListComponent; const data = [e1]; #// Will trigger CD f({ data: data }); data.push(e2); #// Will not trigger CD f({ data: data }); #// Will trigger CD f({ data: data.slice() });

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Pseudo code (not Angular) const f = EmployeeListComponent; const data = [e1]; #// Will trigger CD f({ data: data }); data.push(e2); #// Will not trigger CD f({ data: data }); #// Will trigger CD f({ data: data.slice() });

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twitter.com/mgechev Passing new reference triggers the change detection

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twitter.com/mgechev Should we copy the array every time?

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Why would we do that…?

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twitter.com/mgechev Immutable.js helps: • We get a new reference on change • We do not copy the entire data structure

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@Component({ template: ` # ` }) export class AppComponent implements OnInit { list: List; add(list: List, name: string) { return list.unshift({ label: name, num: ##... }); } remove(list: List, node: EmployeeData) { return list.splice(list.indexOf(node), 1); } }

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@Component({ template: ` # ` }) export class AppComponent implements OnInit { list: List; add(list: List, name: string) { return list.unshift({ label: name, num: ##... }); } remove(list: List, node: EmployeeData) { return list.splice(list.indexOf(node), 1); } }

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@Component({ template: ` # ` }) export class AppComponent implements OnInit { list: List; add(list: List, name: string) { return list.unshift({ label: name, num: ##... }); } remove(list: List, node: EmployeeData) { return list.splice(list.indexOf(node), 1); } }

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twitter.com/mgechev Lets see how fast it is now!

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Non Optimized On Push Typing Speed

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2x faster but still slow…

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AppComponent EmployeeListComponenet (sales) EmployeeListComponenet (r&d) E1 E2 En … E1 E2 En … Ignored details for simplicity

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AppComponent EmployeeListComponenet (sales) EmployeeListComponenet (r&d) E1 E2 En … E1 E2 En … Ignored details for simplicity

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AppComponent EmployeeListComponenet (sales) EmployeeListComponenet (r&d) E1 E2 En … E1 E2 En … Ignored details for simplicity

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AppComponent EmployeeListComponenet (sales) EmployeeListComponenet (r&d) E1 E2 En … E1 E2 En … Ignored details for simplicity

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AppComponent EmployeeListComponenet (sales) EmployeeListComponenet (r&d) E1 E2 En … E1 E2 En … Ignored details for simplicity

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AppComponent EmployeeListComponenet (sales) EmployeeListComponenet (r&d) E1 E2 En … E1 E2 En … Ignored details for simplicity

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twitter.com/mgechev With OnPush change detection will be triggered when the framework, with reference check, determines that any of the inputs of a component has changed…or when an event in the component is triggered

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twitter.com/mgechev Lets do some refactoring!

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AppComponent EmployeesListComponent NameInputComponent ListComponent

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AppComponent EmployeesListComponent NameInputComponent ListComponent

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AppComponent EmployeesListComponent NameInputComponent ListComponent

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twitter.com/mgechev Sooo much faster!

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AppComponent EmployeeListComponenet (sales) EmployeeListComponenet (r&d) E1 E2 En … E1 E2 En … ListComponenet (sales) ListComponenet (r&d) Ignored details for simplicity

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AppComponent EmployeeListComponenet (sales) EmployeeListComponenet (r&d) E1 E2 En … E1 E2 En … ListComponenet (sales) ListComponenet (r&d) Ignored details for simplicity

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AppComponent EmployeeListComponenet (sales) EmployeeListComponenet (r&d) E1 E2 En … E1 E2 En … ListComponenet (sales) ListComponenet (r&d) Ignored details for simplicity

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AppComponent EmployeeListComponenet (sales) EmployeeListComponenet (r&d) E1 E2 En … E1 E2 En … ListComponenet (sales) ListComponenet (r&d) Ignored details for simplicity

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Unoptimized Refactored with On Push Typing Speed

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Adding items

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AppComponent EmployeeListComponenet (sales) E1 E2 En … ListComponenet (sales) Ignored details for simplicity

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AppComponent EmployeeListComponenet (sales) E1 E2 En … ListComponenet (sales) Ignored details for simplicity

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AppComponent EmployeeListComponenet (sales) E1 E2 En … ListComponenet (sales) Ignored details for simplicity

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AppComponent EmployeeListComponenet (sales) E1 E2 En … ListComponenet (sales) E0 Ignored details for simplicity

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twitter.com/mgechev Recomputing everything every time we add a new entry

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const fibonacci = n #=> { if (n ##=== 1 #|| n ##=== 2) return 1; return fibonacci(n - 1) + fibonacci(n - 2); };

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// Two properties // - No side effects // - Same result for same arguments const fibonacci = n #=> { if (n ##=== 1 #|| n ##=== 2) return 1; return fibonacci(n - 1) + fibonacci(n - 2); };

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twitter.com/mgechev Pure Function

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twitter.com/mgechev Pipes in Angular • Pure • Impure

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twitter.com/mgechev Angular executes a pure pipe only when it detects a change to the input value. A pure change is either a change to a primitive input value (String, Number, Boolean, Symbol) or a changed object reference (Date, Array, Function, Object).

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twitter.com/mgechev Angular treats expressions with pure pipes as referentially transparent

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{{ birthday | date }} {{ birthday | impureDate }}

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{{ birthday | date }} {{ birthday | impureDate }} i1.ɵunv(_v, 1, 0, _ck(_v, 2, 0, i1.ɵnov(_v, 0), _co.birthday)); i1.ɵunv(_v, 1, 1, i1.ɵnov(_v, 3).transform(_co.birthday));

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{{ birthday | date }} {{ birthday | impureDate }} i1.ɵunv(_v, 1, 0, _ck(_v, 2, 0, i1.ɵnov(_v, 0), _co.birthday)); i1.ɵunv(_v, 1, 1, i1.ɵnov(_v, 3).transform(_co.birthday));

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@Pipe({ name: 'calculate', pure: true }) export class CalculatePipe { transform(num: number) { return fibonacci(num); } }

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@Component({ changeDetection: ChangeDetectionStrategy.OnPush, template: ` ##... {{ item.num | calculate }} ##... ` }) export class ListComponent { ##... }

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twitter.com/mgechev Lets benchpress it!

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Refactored with On Push Calculation in a Pure Pipe Adding / Removing Entries

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twitter.com/mgechev Initial rendering… with 1000 items

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twitter.com/mgechev Lets take a look at our data

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fibonacci(27)

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fibonacci(27) fibonacci(28)

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fibonacci(27) fibonacci(28) fibonacci(29)

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twitter.com/mgechev Samples from a small range During initial rendering we recompute same value multiple times

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twitter.com/mgechev Solution Caching the value once computed

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twitter.com/mgechev Memoization

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twitter.com/mgechev Memoization possible for pure functions

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const memoize = require('lodash.memoize'); const fibonacci = memoize((num: number): number #=> { if (num ##=== 1 #|| num ##=== 2) return 1; return fibonacci(num - 1) + fibonacci(num - 2); });

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const memoize = require('lodash.memoize'); const fibonacci = memoize((num: number): number #=> { if (num ##=== 1 #|| num ##=== 2) return 1; return fibonacci(num - 1) + fibonacci(num - 2); });

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Pure Pipe Pure Pipe & Memoization Initial Rendering

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Pure Pipes 27 | calculate 27 | calculate 27 | calculate

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Pure Pipes 27 | calculate 27 | calculate 27 | calculate fib(27) 196418

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Pure Pipes 27 | calculate 27 | calculate 27 | calculate fib(27) fib(27) 196418 196418

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Pure Pipes 27 | calculate 27 | calculate 27 | calculate fib(27) fib(27) fib(27) 196418 196418 196418

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Memoization 27 | calculate 27 | calculate 27 | calculate

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27 | calculate 27 | calculate 27 | calculate fib(27) 196418 Memoization

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27 | calculate 27 | calculate 27 | calculate fib(27) 196418 cache Memoization 27

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27 | calculate 27 | calculate 27 | calculate fib(27) 196418 cache fib(27) Memoization 27 27

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27 | calculate 27 | calculate 27 | calculate fib(27) 196418 cache fib(27) 196418 Memoization 27 27

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27 | calculate 27 | calculate 27 | calculate fib(27) 196418 cache fib(27) 196418 fib(27) Memoization 27 27 27

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27 | calculate 27 | calculate 27 | calculate fib(27) 196418 cache fib(27) 196418 fib(27) 196418 Memoization 27 27 27

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twitter.com/mgechev Pattern… • On push performs “memoization” • Pure pipes are “memoized”

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twitter.com/mgechev Pattern… for their last input • On push performs “memoization” • Pure pipes are “memoized”

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twitter.com/mgechev Lets try to do better!

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How NgForOf works @Directive({selector: '[ngFor][ngForOf]'}) class NgForOf implements DoCheck, OnChanges { ##... constructor(private _differs: IterableDiffers) {} ngDoCheck(): void { const changes = this._differ.diff(this.ngForOf); if (changes) this._applyChanges(changes); } ##... }

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How NgForOf works @Directive({selector: '[ngFor][ngForOf]'}) class NgForOf implements DoCheck, OnChanges { ##... constructor(private _differs: IterableDiffers) {} ngDoCheck(): void { const changes = this._differ.diff(this.ngForOf); if (changes) this._applyChanges(changes); } ##... }

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class IterableDiffers { constructor(factories: IterableDifferFactory[]) {} find(iterable: any): IterableDifferFactory { const factory = this.factories.find(f #=> f.supports(iterable)); if (factory #!= null) { return factory; } else { throw new Error( `Cannot find a differ supporting object` ); } } #// ##... }

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interface IterableDifferFactory { supports(objects: any): boolean; create(trackByFn#?: TrackByFunction): IterableDiffer; } interface IterableDiffer { diff(object: NgIterable): IterableChanges|null; } interface TrackByFunction { (index: number, item: T): any; }

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interface IterableDifferFactory { supports(objects: any): boolean; create(trackByFn#?: TrackByFunction): IterableDiffer; } interface IterableDiffer { diff(object: NgIterable): IterableChanges|null; } interface TrackByFunction { (index: number, item: T): any; }

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interface IterableDifferFactory { supports(objects: any): boolean; create(trackByFn#?: TrackByFunction): IterableDiffer; } interface IterableDiffer { diff(object: NgIterable): IterableChanges|null; } interface TrackByFunction { (index: number, item: T): any; }

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interface IterableDifferFactory { supports(objects: any): boolean; create(trackByFn#?: TrackByFunction): IterableDiffer; } interface IterableDiffer { diff(object: NgIterable): IterableChanges|null; } interface TrackByFunction { (index: number, item: T): any; }

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IterableDiffers IterableDifferFactory IterableDiffer TrackByFn NgForOf Injects Uses Uses Uses Sets Creates

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IterableDiffers IterableDifferFactory IterableDiffer TrackByFn NgForOf Injects Uses Uses Uses Sets Creates

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IterableDiffers IterableDifferFactory IterableDiffer TrackByFn NgForOf Injects Uses Uses Uses Sets Creates

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IterableDiffers IterableDifferFactory IterableDiffer TrackByFn NgForOf Injects Uses Uses Uses Sets Creates

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IterableDiffers IterableDifferFactory IterableDiffer TrackByFn NgForOf Injects Uses Uses Uses Sets Creates

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How NgForOf works @Directive({selector: '[ngFor][ngForOf]'}) class NgForOf implements DoCheck, OnChanges { ##... constructor(private _differs: IterableDiffers) {} ngDoCheck(): void { const changes = this._differ.diff(this.ngForOf); if (changes) this._applyChanges(changes); } ##... }

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const a = [ { id: 1, name: 'Dan' }, { id: 2, name: 'Joe' }, { id: 3, name: 'Josh' } ]; const b = [ { id: 1, name: 'Dan' }, { id: 2, name: 'Adam' }, { id: 4, name: 'Josh' } ]; const trackBy = (_, item) #=> item.id; cmp(trackBy(0, a[0]), trackBy(0, b[0])) cmp(trackBy(1, a[1]), trackBy(1, b[1])) cmp(trackBy(2, a[2]), trackBy(2, b[2])) Identical Ignored details for simplicity

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cmp(trackBy(0, a[0]), trackBy(0, b[0])) cmp(trackBy(1, a[1]), trackBy(1, b[1])) cmp(trackBy(2, a[2]), trackBy(2, b[2])) Identical const a = [ { id: 1, name: 'Dan' }, { id: 2, name: 'Joe' }, { id: 3, name: 'Josh' } ]; const b = [ { id: 1, name: 'Dan' }, { id: 2, name: 'Adam' }, { id: 4, name: 'Josh' } ]; const trackBy = (_, item) #=> item.id; trackBy(0, a[0]) ##=== trackBy(0, b[0]) cmp(trackBy(1, a[1]), trackBy(1, b[1])) cmp(trackBy(2, a[2]), trackBy(2, b[2])) ✅ ✅ ❌ Ignored details for simplicity

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cmp(trackBy(0, a[0]), trackBy(0, b[0])) cmp(trackBy(1, a[1]), trackBy(1, b[1])) cmp(trackBy(2, a[2]), trackBy(2, b[2])) Identical const trackBy = (_, item) #=> item.id; ✅ ✅ ❌ const a = [ { id: 1, name: 'Dan' }, { id: 2, name: 'Joe' }, { id: 3, name: 'Josh' } ]; const b = [ { id: 1, name: 'Dan' }, { id: 2, name: 'Adam' }, { id: 4, name: 'Josh' } ]; trackBy(0, a[0]) ##=== trackBy(0, b[0]) trackBy(1, a[1]) ##=== trackBy(1, b[1]) cmp(trackBy(2, a[2]), trackBy(2, b[2])) Ignored details for simplicity

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cmp(trackBy(0, a[0]), trackBy(0, b[0])) cmp(trackBy(1, a[1]), trackBy(1, b[1])) cmp(trackBy(2, a[2]), trackBy(2, b[2])) Identical const trackBy = (_, item) #=> item.id; ✅ ✅ ❌ const a = [ { id: 1, name: 'Dan' }, { id: 2, name: 'Joe' }, { id: 3, name: 'Josh' } ]; const b = [ { id: 1, name: 'Dan' }, { id: 2, name: 'Adam' }, { id: 4, name: 'Josh' } ]; trackBy(0, a[0]) ##=== trackBy(0, b[0]) trackBy(1, a[1]) ##=== trackBy(1, b[1]) trackBy(2, a[2]) ##=== trackBy(2, b[2]) cmp(trackBy(2, a[2]), trackBy(2, b[2])) Ignored details for simplicity

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twitter.com/mgechev IterableDiffer checks from the outside whether the data structure has changed

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twitter.com/mgechev But the data structure knows that best!

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export class DifferableList { changes = new LinkedList>(); constructor(private data = List([])) {} unshift(data: T) { const result = new DifferableList(this.data.unshift(data)); result.changes.add({ ##... }); return result; } ##... [Symbol.iterator]() { return new DifferableListIterator(this); } }

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export class DifferableList { changes = new LinkedList>(); constructor(private data = List([])) {} unshift(data: T) { const result = new DifferableList(this.data.unshift(data)); result.changes.add({ ##... }); return result; } ##... [Symbol.iterator]() { return new DifferableListIterator(this); } }

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export class DifferableList { changes = new LinkedList>(); constructor(private data = List([])) {} unshift(data: T) { const result = new DifferableList(this.data.unshift(data)); result.changes.add({ ##... }); return result; } ##... [Symbol.iterator]() { return new DifferableListIterator(this); } }

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export class DifferableList { changes = new LinkedList>(); constructor(private data = List([])) {} unshift(data: T) { const result = new DifferableList(this.data.unshift(data)); result.changes.add({ ##... }); return result; } ##... [Symbol.iterator]() { return new DifferableListIterator(this); } }

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export class DifferableList { changes = new LinkedList>(); constructor(private data = List([])) {} unshift(data: T) { const result = new DifferableList(this.data.unshift(data)); result.changes.add({ ##... }); return result; } ##... [Symbol.iterator]() { return new DifferableListIterator(this); } }

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twitter.com/mgechev Data structure optimized for Angular

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export class DifferableListDiffer implements IterableDiffer, IterableChanges { ##... diff(collection: NgIterable): DifferableListDiffer | null { const changes = this._data.changes; this._changes = changes; if (changes.size() > 0) { this._data.changes = new LinkedList>(); return this; } else { return null; } } }

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export class DifferableListDiffer implements IterableDiffer, IterableChanges { ##... diff(collection: NgIterable): DifferableListDiffer | null { const changes = this._data.changes; this._changes = changes; if (changes.size() > 0) { this._data.changes = new LinkedList>(); return this; } else { return null; } } }

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twitter.com/mgechev Required refactoring

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@Component({ selector: 'sd-employee-list', providers: [ IterableDiffers.extend([ new DifferableListDifferFactory() ]) ], template: `##...`, }) export class EmployeeListComponent { ##... }

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twitter.com/mgechev Persistent data structures Inspired by

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Default Differ Custom Differ Adding / Removing Entries

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twitter.com/mgechev Recap • OnPush change detection • When it gets triggered • Pure pipes vs Memoization • Purity and Referential Transparency • Differs and Track by function

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twitter.com/mgechev Lessons learned • No silver bullet • Understand your component structure • Understand your data • Application specific benchmarks

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twitter.com/mgechev Get inspiration from computer science

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twitter.com/mgechev Links mgv.io/ng-cd - Angular’s OnPush Change Detection Strategy mgv.io/ng-pure - Pure Pipes and Referential Transparency mgv.io/ng-diff - Understanding Angular Differs mgv.io/ng-perf-checklist - Angular Performance Checklist mgv.io/ng-checklist-video - Angular Performance Checklist (video)

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Thank you! twitter.com/mgechev github.com/mgechev blog.mgechev.com