Angular 2 + FormArray Access + Demo Plunk

<!DOCTYPE html>
<html>

  <head>
    <base href="." />
    <script type="text/javascript" charset="utf-8">
      window.AngularVersionForThisPlunker = 'latest'
    </script>
    <title>angular playground</title>
    <link rel="stylesheet" href="style.css" />
    <script src="https://unpkg.com/core-js@2.4.1/client/shim.min.js"></script>
    <script src="https://unpkg.com/zone.js/dist/zone.js"></script>
    <script src="https://unpkg.com/zone.js/dist/long-stack-trace-zone.js"></script>
    <script src="https://unpkg.com/reflect-metadata@0.1.3/Reflect.js"></script>
    <script src="https://unpkg.com/systemjs@0.19.31/dist/system.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 */

### Angular Starter Plunker - Typescript

var angularVersion;
if(window.AngularVersionForThisPlunker === 'latest'){
  angularVersion = ''; //picks up latest
}
else {
  angularVersion = '@' + window.AngularVersionForThisPlunker;
}

System.config({
  //use typescript for compilation
  transpiler: 'typescript',
  //typescript compiler options
  typescriptOptions: {
    emitDecoratorMetadata: true
  },
  paths: {
    'npm:': 'https://unpkg.com/'
  },
  //map tells the System loader where to look for things
  map: {
    
    'app': './src',
    '@angular/core': 'npm:@angular/core'+ angularVersion + '/bundles/core.umd.js',
    '@angular/common': 'npm:@angular/common' + angularVersion + '/bundles/common.umd.js',
    '@angular/compiler': 'npm:@angular/compiler' + angularVersion  + '/bundles/compiler.umd.js',
    '@angular/platform-browser': 'npm:@angular/platform-browser' + angularVersion + '/bundles/platform-browser.umd.js',
    '@angular/platform-browser-dynamic': 'npm:@angular/platform-browser-dynamic' + angularVersion + '/bundles/platform-browser-dynamic.umd.js',
    '@angular/http': 'npm:@angular/http' + angularVersion + '/bundles/http.umd.js',
    '@angular/router': 'npm:@angular/router' + angularVersion +'/bundles/router.umd.js',
    '@angular/forms': 'npm:@angular/forms' + angularVersion + '/bundles/forms.umd.js',
    '@angular/animations': 'npm:@angular/animations' + angularVersion + '/bundles/animations.umd.js',
    '@angular/platform-browser/animations': 'npm:@angular/platform-browser' + angularVersion + '/bundles/platform-browser-animations.umd.js',
    '@angular/animations/browser': 'npm:@angular/animations' + angularVersion + '/bundles/animations-browser.umd.js',
    
    '@angular/core/testing': 'npm:@angular/core' + angularVersion + '/bundles/core-testing.umd.js',
    '@angular/common/testing': 'npm:@angular/common' + angularVersion + '/bundles/common-testing.umd.js',
    '@angular/compiler/testing': 'npm:@angular/compiler' + angularVersion + '/bundles/compiler-testing.umd.js',
    '@angular/platform-browser/testing': 'npm:@angular/platform-browser' + angularVersion + '/bundles/platform-browser-testing.umd.js',
    '@angular/platform-browser-dynamic/testing': 'npm:@angular/platform-browser-dynamic' + angularVersion + '/bundles/platform-browser-dynamic-testing.umd.js',
    '@angular/http/testing': 'npm:@angular/http' + angularVersion + '/bundles/http-testing.umd.js',
    '@angular/router/testing': 'npm:@angular/router' + angularVersion + '/bundles/router-testing.umd.js',
    'tslib': 'npm:tslib@1.6.1',
    'rxjs': 'npm:rxjs',
    'typescript': 'npm:typescript@2.2.1/lib/typescript.js'
  },
  //packages defines our app package
  packages: {
    app: {
      main: './main.ts',
      defaultExtension: 'ts'
    },
    rxjs: {
      defaultExtension: 'js'
    }
  }
});

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

platformBrowserDynamic().bootstrapModule(AppModule)

//our root app component
import { Component, NgModule } from '@angular/core'
import { BrowserModule } from '@angular/platform-browser'
import { ReactiveFormsModule } from '@angular/forms';

import { CheckAllComponent ] from './check-all.component';

@Component({
  selector: 'my-app',
  template: `<check-all></check-all>`,
})
export class App {
}

@NgModule({
  imports: [ BrowserModule, ReactiveFormsModule],
  declarations: [ App, CheckAllComponent ],
  bootstrap: [ App ]
})
export class AppModule {}

import { Component } from '@angular/core';
import { FormBuilder, FormGroup } from '@angular/forms';

@Component({
  selector: 'check-all',
  template: `
  <form [formGroup]="groupForm" novalidate>
    <div class="form-group" formGroupName="groupChapters">
      <label for="">Select chapters</label>
      <div *ngFor="let chapter of formChapters.controls; let i = index" class="checkbox">
        <label>
          <input type="checkbox" formControlName="{{i}}">
          {{chapters[i].title}}
        </label>
      </div>
      <button (click)="checkAll()">Check all</button>
    </div>
  </form>`
})
export class CheckAllComponent {
  
  private chapters = [
    {"title":"1. Title", "selected":false},
    {"title":"2. Title", "selected":false},
    {"title":"3. Title", "selected":false},
  ];
    
  constructor(private _formBuilder: FormBuilder) {
    this.buildForm();
    this.formChapters = this.buildChapters();
  }
  
  private checkAll() {
    this.groupForm.controls['groupChapters'].setValue(
      this.groupForm.controls['groupChapters'].value
        .map(value => true);
    );
  }

  private buildForm() {
    this.groupForm = this._formBuilder.group({
      bookId: this._formBuilder.control(null),
      startDate: this._formBuilder.control(null),
      groupTotal: this._formBuilder.control(null),
      chapterGrouping: this._formBuilder.control("all"),
      groupChapters: this.buildChapters()
    });
    
  } 

  private buildChapters() {
    const chapters = this.chapters.map(chapter => {
      return this._formBuilder.control(chapter.selected)
    });
    return this._formBuilder.array(chapters);
  }
}