Angular2 Form validation example, which shows error message for invalid data and disable the form submit button as well.

<!DOCTYPE html>
<html>

  <head>
    <base href="." />
    <link rel="stylesheet" href="https://www.w3schools.com/w3css/4/w3.css">
    <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@0.8.12/dist/zone.js"></script>
    <script src="https://unpkg.com/zone.js@0.8.12/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 */
body{
  background-color: #9A9BCE;
}
.invalidData1 {
  color: red;
  font-size: 14px;
}

.invalidData2 {
  background-color: #E98787;
  color: white;
}

.form {
  padding: 5px;
  border: 1px solid #f2f2f2;
  background-color: #f2f2f2;
  border-radius: 5px;
}

### Angular Starter Plunker - Typescript




This Plunker example shows how to validate user input in the UI and display 
useful validation messages using Template Driven Forms approach. It is 
also an example of Angular 2-way data binding







###               https://www.learn-angular2.com                       ###

###               Author : Abhishek Jha                                ###

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, VERSION} from '@angular/core'
import {BrowserModule} from '@angular/platform-browser'
import { FormsModule }   from '@angular/forms';

@Component({
  selector: 'my-app',
  templateUrl: `src/app.html`,
})
export class App {
  model1 = {
    username: "",
    email: "",
    comment: ""
  };
  model2 = {
    username: "",
    email: "",
    comment: ""
  };
  constructor() {
    
  }
}

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

<p><b>Note: Enter the data to see the difference between both the forms.</b></p>

<div class="w3-col l6 m8 s12 form">
  <h3>First Form</h3>
<form class="w3-container" name="contactForm1" #contactForm1="ngForm" method="POST" novalidate>
                <p>
                <label for="username">Name</label>
                <input class="w3-input" type="text" name="username1" id="name" required minlength="4" maxlength="24" [(ngModel)]="model1.username" #username1="ngModel"></p>
                    <div *ngIf="username1.errors && (username1.dirty || username1.touched)" class="invalidData1">
                        <div [hidden]="!username1.errors.required">
                            Name is required
                        </div>
                        <div [hidden]="!username1.errors.minlength">
                            Name must be at least 4 characters long.
                        </div>
                        <div [hidden]="!username1.errors.maxlength">
                            Name cannot be more than 24 characters long.
                        </div>
                    </div>
                
                <p>
                <label>Email</label>
                <input class="w3-input" type="email" name="email1" id="email" required minlength="4" maxlength="30" [(ngModel)]="model1.email" #email1="ngModel"></p>
                <div *ngIf="email1.errors && (email1.dirty || email1.touched)" class="invalidData1">
                        <div [hidden]="!email1.errors.required">
                            Email is required
                        </div>
                        <div [hidden]="!email1.errors.minlength">
                            Email must be at least 4 characters long.
                        </div>
                        <div [hidden]="!email1.errors.maxlength">
                            Email cannot be more than 30 characters long.
                        </div>
                    </div>
                <p>
                <label>Comment</label>
                <textarea class="w3-input" rows="4" cols="50" id="comment" required minlength="4" maxlength="500" name="comment1" [(ngModel)]="model1.comment" #comment1="ngModel">                      
                </textarea></p>
                         <div *ngIf="comment1.errors && (comment1.dirty || comment1.touched)" class="invalidData1">
                                <div [hidden]="!comment1.errors.required">
                                Comment is required
                                </div>
                                <div [hidden]="!comment1.errors.minlength">
                                Comment must be at least 4 characters long.
                                </div>
                                <div [hidden]="!comment1.errors.maxlength">
                                Comment cannot be more than 500 characters long.
                                </div>
                            </div>

            <button type="submit" class="w3-button w3-round w3-right w3-teal" [disabled]="!contactForm1.form.valid">Submit</button>
                </form>
                
            </div>

<div class="w3-col l6 m8 s12 form">
  <h3>Second Form</h3>
<form class="w3-container" name="contactForm2" #contactForm2="ngForm" method="POST" novalidate>
                <p>
                <label for="username">Name</label>
                <input class="w3-input" type="text" name="username2" [ngClass]="{'invalidData2': username2.errors && (username2.dirty || username2.touched)}" required minlength="4" maxlength="24" [(ngModel)]="model2.username" #username2="ngModel"></p>
                <p>
                <label>Email</label>
                <input class="w3-input" type="email" name="email2" [ngClass]="{'invalidData2': email2.errors && (email2.dirty || email2.touched)}" required minlength="4" maxlength="30" [(ngModel)]="model2.email" #email2="ngModel"></p>
                <p>
                <label>Comment</label>
                <textarea class="w3-input" rows="4" cols="50" [ngClass]="{'invalidData2': comment2.errors && (comment2.dirty || comment2.touched)}" required minlength="4" maxlength="500" name="comment2" [(ngModel)]="model2.comment" #comment2="ngModel">                      
                </textarea></p>

            <button type="submit" class="w3-button w3-round w3-right w3-teal" [disabled]="!contactForm2.form.valid">Submit</button>
                </form>
                </div>