Simple callout Angular 2 directive

<!DOCTYPE html>
<html>

  <head>
    <base href="." />
    <title>Angular App</title>
    
    <style>
        my-app {
            font-size: 1.2em;
        }
        
        input[type=checkbox] {
            width: 20px;
            height: 20px;
            cursor: pointer;
        }
    </style>
    
     <!-- polyfill(s) for older browsers -->
    <script src="https://unpkg.com/core-js/client/shim.min.js"></script>

    <script src="https://unpkg.com/zone.js@0.8.16?main=browser"></script>
    <!--<script src="https://unpkg.com/reflect-metadata@0.1.10"></script>-->
    <script src="https://unpkg.com/systemjs@0.20.18/dist/system.src.js"></script>
    <script src="https://unpkg.com/web-animations-js@2.3.1"></script>
  

    <script src="systemjs.config.js"></script>
    <script>
        System.import('app').catch(function (err) { console.error(err); });
    </script>
  </head>

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

</html>

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

@Component({
  selector: 'my-app',
  template: `
    <p>Hover over the buttons to see hints in callouts.</p>
    <button [appCallout]="'Ask the all-seeing goat wizard'">What do I do?</button>
    <button [appCallout]="'Crab walk with some crabs'">Mystery button</button>
    <button [appCallout]="'Deploy the thousand-year back hair'">Don't push me</button>
  `,
  styles: [`
   
  `]
})
export class AppComponent {
  public isReadOnly: boolean = false;
}

import { NgModule } from '@angular/core';
import { FormsModule } from '@angular/forms';
import { BrowserModule } from '@angular/platform-browser';
import { BrowserAnimationsModule } from '@angular/platform-browser/animations';
import { AppComponent } from './app.component';
import { CalloutComponent } from './callout.component';
import { CalloutDirective } from './callout.directive';

@NgModule({
    imports: [
        BrowserModule,
        BrowserAnimationsModule,
        FormsModule,
    ],
    declarations: [
        AppComponent,
        CalloutComponent,
        CalloutDirective,
    ],
    entryComponents: [
        CalloutComponent
    ],
    providers: [
      
    ],
    bootstrap: [AppComponent]
})
export class AppModule { }

(function (global) {
  var angVer = '5.0.0-beta.6';
 
  System.config({
    transpiler: 'ts',
    typescriptOptions: {
      "emitDecoratorMetadata": true,
      "experimentalDecorators": true,
      "lib": [ "es2015", "dom" ],
      "module": "commonjs",
      "moduleResolution": "node",
      "noImplicitAny": true,
      "sourceMap": true,
      "suppressImplicitAnyIndexErrors": true,
      "target": "es5"
    },
    meta: {
      'typescript': {
        "exports": "ts"
      }
    },
    paths: { 
      'npm:': 'https://unpkg.com/',
      'gh:': 'https://raw.githubusercontent.com/'
    },
    map: {
      "app": "app",
      "rxjs": "npm:rxjs@5.4.3",
      "ts": "npm:plugin-typescript@7.1.0/lib/plugin.js",
      "typescript": "npm:typescript@2.4.2/lib/typescript.js",
      "@angular/core": "npm:@angular/core@" + angVer + "/bundles/core.umd.js",
      "@angular/common": "npm:@angular/common@" + angVer + "/bundles/common.umd.js",
      "@angular/compiler": "npm:@angular/compiler@" + angVer + "/bundles/compiler.umd.js",
      "@angular/platform-browser": "npm:@angular/platform-browser@" + angVer + "/bundles/platform-browser.umd.js",
      "@angular/platform-browser-dynamic": "npm:@angular/platform-browser-dynamic@" + angVer + "/bundles/platform-browser-dynamic.umd.js",
      "@angular/http": "npm:@angular/http@" + angVer + "/bundles/http.umd.js",
      "@angular/router": "npm:@angular/router@" + angVer + "/bundles/router.umd.js",
      "@angular/forms": "npm:@angular/forms@" + angVer + "/bundles/forms.umd.js",
      "@angular/animations": "npm:@angular/animations@" + angVer + "/bundles/animations.umd.js",
      "@angular/animations/browser": "npm:@angular/animations@" + angVer + "/bundles/animations-browser.umd.js",
      "@angular/platform-browser/animations": "npm:@angular/platform-browser@" + angVer + "/bundles/platform-browser-animations.umd.js",
      "@angular/flex-layout": "npm:@angular/flex-layout@2.0.0-beta.9"
},
    // packages tells the System loader how to load when no filename and/or no extension
    packages: {
      app: {
        main: './main.ts',
        defaultExtension: 'ts'
      },
      rxjs: {
        defaultExtension: 'js'
      }
    }
  });

  if (!global.noBootstrap) { bootstrap(); }

  // Bootstrap the `AppModule`(skip the `app/main.ts` that normally does this)
  function bootstrap() {

    // Stub out `app/main.ts` so System.import('app') doesn't fail if called in the index.html
    System.set(System.normalizeSync('app/main.ts'), System.newModule({ }));

    // bootstrap and launch the app (equivalent to standard main.ts)
    Promise.all([
      System.import('@angular/platform-browser-dynamic'),
      System.import('app/app.module')
    ])
    .then(function (imports) {
      var platform = imports[0];
      var app      = imports[1];
      platform.platformBrowserDynamic().bootstrapModule(app.AppModule);
    })
    .catch(function(err){ console.error(err); });
  }
})(this);

import {
    ChangeDetectorRef,
    Directive,
    EventEmitter,
    ElementRef,
    Input,
    NgZone,
    OnChanges,
    OnDestroy,
    Optional,
    Output,
    SkipSelf,
    ViewContainerRef,
    ComponentFactoryResolver
} from '@angular/core';

import {CalloutComponent} from './callout.component';

class Point {
    constructor(public x: number, public y: number) {};
}

@Directive({
    selector: '[appCallout]',
    host: {
        '(mouseenter)': 'showCallout()',
        '(mouseleave)': 'hideCallout()'
    }
})
export class CalloutDirective implements OnDestroy, OnChanges {
    @Input() appCallout: String = '';
    
    private element: HTMLElement;
    private calloutRef: ComponentRef<CalloutComponent>;

    constructor(
        private elementRef: ElementRef,
        private viewContainer: ViewContainerRef,
        private componentFactoryResolver: ComponentFactoryResolver,
        @Optional() private changeDetector: ChangeDetectorRef,
        @Optional() private zone: NgZone,
    ) {

    }
    
    ngOnInit() {
        this.element = this.elementRef.nativeElement;
    }

    ngOnDestroy() {
        this.hideCallout();
        super.onDestroy();
    }

    showCallout() {
        this.calloutRef = this.createCallout(this.appCallout);
        let calloutEl = this.calloutRef.location.nativeElement;
        let targetPos = this.getTargetCalloutLocation();
        calloutEl.style.left = targetPos.x + 'px';
        calloutEl.style.top = targetPos.y + 'px';
    }
    
    hideCallout() {
        if (this.calloutRef) {
            this.calloutRef.destroy();
            this.calloutRef = null;    
        }
    }
    
    private createCallout(content: Stirng): ComponentRef<CalloutComponent> {
        this.viewContainer.clear();

        let calloutComponentFactory = 
          this.componentFactoryResolver.resolveComponentFactory(CalloutComponent);
        let calloutComponentRef = this.viewContainer.createComponent(calloutComponentFactory);

        calloutComponentRef.instance.content = content;

        return calloutComponentRef;
    }
    
    private getTargetCalloutLocation(): Point {
        let box = this.element.getBoundingClientRect();
        return new Point(box.left + box.width / 2, box.bottom + 5);
    }
}

import { 
    Component, 
    NgModule, 
    VERSION, 
    Optional, 
    ChangeDetectorRef
} from '@angular/core'

@Component({
  selector: 'app-callout',
  template: `
        {{content}}
  `,
  styles: [`
    :host {
        background: white;
        padding: 0.2em;
        border: solid 1px #444;
        position: absolute;
        font-size: 14px;
    }
  `]
})
export class CalloutComponent {
    public content: String = '';
}