enum.md

Enum

• ChangeDetectionStrategy

---

ChangeDetectionStrategy

Describes within the change detector which strategy will be used the next time change detection is triggered.

It works only with @Components which have bound properties via one way data binding @Input('<').

Using OnPush is much more convenient than manually declaring ngOnChanges and copying binding values there, so we get immutable data Under the hood it just calls angular.copy and assigns that new binding reference value to component property

members

members	Type	Description
OnPush	enum	OnPush means that the change detector's mode will be set to CheckOnce during hydration
Default	enum	This strategy has every component by default for one way data bound properties. Default means that the change detector's mode will be set to CheckAlways during hydration.

example:

import { Component, Input, OnChanges, ChangeDetectionStrategy } from 'ng-metadata/core';
import { User } from './user.model';

@Component( {
  selector: 'child',
  changeDetection: ChangeDetectionStrategy.OnPush,
  template: `
    <div>
      <input type="text" ng-model="$ctrl.user.name">
    </div>
  `
} )
export class ChildComponent implements OnChanges {

  // without OnPush if we change some property on this object in the parent, it will mutate also within child,
  // because that's how javascript works (Objects are passed reference baby!)
  // => this is not true if the bounded property is a primitive ( again this is how JS works)
  @Input('<') user: User;

  ngOnChanges( changes ) {
    if(changes.user){
      // this will execute only when user reference has changed on parent
      console.log(changes.user);
    }
  }

}