ATScript explain the OnPush strategy of ChangeDetectionStrategy

<!DOCTYPE html>
<html>

  <head>
    <title>angular2 playground</title>
    <link rel="stylesheet" href="style.css" />
    <script src="https://code.angularjs.org/2.0.0-beta.17/angular2-polyfills.js"></script>
    <script src="https://code.angularjs.org/tools/system.js"></script>
    <script src="https://code.angularjs.org/tools/typescript.js"></script>
    <script src="config.js"></script>
    <script>
    System.import('app')
      .catch(console.error.bind(console));
  </script>
  </head>

  <body>
    <my-app>
    loading...
  </my-app>
  </body>

</html>

/* Styles go here */

### Angular2  - Typescript - RC.0
>* when to use ChangeDetectionStrategy.OnPush
>* how to trigger the chagnes detect for component with OnPush
>* other approch to triger change detect besides the Input Change
>* note what the 'change' means, it is the reference change, not object chagne

System.config({
  //use typescript for compilation
  transpiler: 'typescript',
  //typescript compiler options
  typescriptOptions: {
    emitDecoratorMetadata: true
  },
  //map tells the System loader where to look for things
  map: {
    app: "./src",
    '@angular': 'https://npmcdn.com/@angular',
    'rxjs': 'https://npmcdn.com/rxjs@5.0.0-beta.6'
  },
  //packages defines our app package
  packages: {
    app: {
      main: './main.ts',
      defaultExtension: 'ts'
    },
    '@angular/core': {
      main: 'bundles/core.umd.js',
      defaultExtension: 'js'
    },
    '@angular/compiler': {
      main: 'bundles/compiler.umd.js',
      defaultExtension: 'js'
    },
    '@angular/common': {
      main: 'bundles/common.umd.js',
      defaultExtension: 'js'
    },
    '@angular/platform-browser-dynamic': {
      main: 'bundles/platform-browser-dynamic.umd.js',
      defaultExtension: 'js'
    },
    '@angular/platform-browser': {
      main: 'bundles/platform-browser.umd.js',
      defaultExtension: 'js'
    },
    rxjs: {
      defaultExtension: 'js'
    }
  }
});

//main entry point
import {bootstrap} from '@angular/platform-browser-dynamic';
import {App} from './app';

bootstrap(App, [])
  .catch(err => console.error(err));

//our root app component
import {Component,ChangeDetectionStrategy,ChangeDetectorRef,Input} from '@angular/core'

 

@Component({
  selector: 'child',
  /**********************
  OnPush will only trigger change detection 
        when an input property has been changed(in parent) as 
        the result of a change detection check./
    **********************/
  changeDetection: ChangeDetectionStrategy.OnPush,

  template: `<div *ngFor="let hero of heros">{{hero}}</div>`
})
class Child {
  @Input() heros:Observable<[]>;
  constructor(public ref:ChangeDetectorRef){
       // change won't be detected,please consider why 
       setTimeout(()=>{
             this.heros = ['Change',"from ","child, wont show"];
         },2000);
        //  
        setTimeout(()=>{
             this.heros = ['Change',"from ","child, shows up ....yep"];
        //   CONSIDER why this works
             this.ref.markForCheck();
            //  and this doesn't work
            // this.ref.detectChanges();
     
             
         },5000);
  }
}



@Component({
  selector: 'my-app',
  template: `
    <child [heros]="herosArr"><child>
  `,
/*  here you can't use this strategy ,please consider why*/
    // changeDetection: ChangeDetectionStrategy.OnPush,
  directives: [Child]
})
export class App {
    herosArr:[]=['Init','value']
    
    constructor(){
        // change will be detected 
        setTimeout(()=>{
             this.herosArr = ['new ','array','reference','in parent'];
         },1000);
         // change won't be detected,please consider why 
          setTimeout(()=>{
             this.herosArr.push ['append','something','not reflect on page'];
         },3000);
         // change will be detected
          setTimeout(()=>{
             this.herosArr = ['end..........'];
         },4000);
    }
}