Manual validation with ngbDatePicker directive from https://ng-bootstrap.github.io

<!DOCTYPE html>
<html>

  <head>
  <base href="." />
    <title>ng-bootstrap demo</title>
    <link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0-alpha.6/css/bootstrap.min.css" />
    <script src="https://unpkg.com/zone.js@^0.6.23/dist/zone.js"></script>
    <script src="https://unpkg.com/zone.js@^0.6.23/dist/long-stack-trace-zone.js"></script>
    <script src="https://unpkg.com/reflect-metadata@^0.1.8/Reflect.js"></script>
    <script src="https://unpkg.com/systemjs@^0.19.40/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>

var ver = {
    ng: '2.0.0',
    ngRouter: '3.0.0'
  };
  
  System.config({
  //use typescript for compilation
  transpiler: 'typescript',
  //typescript compiler options
  typescriptOptions: {
    emitDecoratorMetadata: true
  },
  paths: {
    'npm:': 'https://unpkg.com/'
  },
  map: {

    'app': './src',

    '@angular/core': 'npm:@angular/core@' + ver.ng + '/bundles/core.umd.js',
    '@angular/common': 'npm:@angular/common@' + ver.ng + '/bundles/common.umd.js',
    '@angular/compiler': 'npm:@angular/compiler@' + ver.ng + '/bundles/compiler.umd.js',
    '@angular/platform-browser': 'npm:@angular/platform-browser@' + ver.ng + '/bundles/platform-browser.umd.js',
    '@angular/platform-browser-dynamic': 'npm:@angular/platform-browser-dynamic@' + ver.ng + '/bundles/platform-browser-dynamic.umd.js',
    '@angular/http': 'npm:@angular/http@' + ver.ng + '/bundles/http.umd.js',
    '@angular/router': 'npm:@angular/router@' + ver.ngRouter + '/bundles/router.umd.js',
    '@angular/forms': 'npm:@angular/forms@' + ver.ng + '/bundles/forms.umd.js',

    'rxjs': 'npm:rxjs@5.0.0-beta.12',
    'typescript': 'npm:typescript@2.0.10/lib/typescript.js',

    '@ng-bootstrap/ng-bootstrap': 'npm:@ng-bootstrap/ng-bootstrap@1.0.0-alpha.18/bundles/ng-bootstrap.js'
  },
  packages: {
    app: {
      main: './main.ts',
      defaultExtension: 'ts'
    },
    rxjs: {
      defaultExtension: 'js'
    }
  }
});

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

platformBrowserDynamic().bootstrapModule(AppModule);


import { Component, NgModule } from '@angular/core';
import { BrowserModule } from '@angular/platform-browser';
import { FormsModule, ReactiveFormsModule. FormControl, Validators } from '@angular/forms';
import { NgbModule } from '@ng-bootstrap/ng-bootstrap';

@Component({
  selector: 'my-app',
  template: `
    <form (ngSubmit)="submit()" #myForm="ngForm">
      <!-- WITHOUT DATEPICKER -->
      <label>Name: </label>
      <input type="text" 
         id="name" 
         class="form-control"
         required 
         minlength="4" 
         maxlength="24"
         name="name" 
         [(ngModel)]="mymodel" 
         style="width:200px"
         #name="ngModel" >
  
      <div *ngIf="name.errors && (name.dirty || name.touched)"
           class="alert alert-danger">
          <div [hidden]="!name.errors.required">
            Name is required
          </div>
          <div [hidden]="!name.errors.minlength">
            Name must be at least 4 characters long.
          </div>
          <div [hidden]="!name.errors.maxlength">
            Name cannot be more than 24 characters long.
          </div>
      </div>
      <br>
    
      <!-- WITH DATEPICKER -->
      <label>Date: </label>
      <input type="text" 
          id="date1" 
          style="width:200px"
          class="form-control"
          [formControl]="control"
          required 
          name="date1" 
          [(ngModel)]="mymodel2"
          (keyup)="manualValidation(dpTest)"
          ngbDatepicker
          #dpTest="ngbDatepicker">
      <button (click)="dpTest.toggle()">
        Cal
      </button>
  
      <div *ngIf="!control.valid" class="alert alert-danger">
        <div>
          Date is of an invalid format
        </div>
      </div>
      <button type="submit">Submit</button>
    </form>
      
  `
})
export class App {

  control: FormControl = new FormControl('date1', Validators.minLength(4));
  
  mymodel2 = {year: 2000, month: 1, day: 1}

  mymodel
  
  constructor() {
    this.mymodel = ""
  }
  
  manualValidation(dpTest) {
    console.log("value of input field: "+dpTest._elRef.nativeElement.value)
    console.log("control.valid before manual validation: "+this.control.valid)
    if (dpTest._elRef.nativeElement.value.length < 4) {
      this.control.setErrors({
        "notMinLength": true
      })
    }
    console.log("control.valid after manual validation: "+this.control.valid)
  }
  
  submit() {
    console.log("submitted")
  }
  
}   

@NgModule({
  imports: [BrowserModule, FormsModule, ReactiveFormsModule, NgbModule.forRoot()], 
  declarations: [App]
  bootstrap: [App]
}) 
export class AppModule {}