Example usage of the tooltip widget 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-beta.2/css/bootstrap.min.css" />
    <script src="https://unpkg.com/core-js@^2.4.1/client/shim.js"></script>
    <script src="https://unpkg.com/zone.js@0.8.10/dist/zone.js"></script>
    <script src="https://unpkg.com/zone.js@0.8.10/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: '5.0.2'
  };
  
  System.config({
  //use typescript for compilation
  transpiler: 'typescript',
  //typescript compiler options
  typescriptOptions: {
    emitDecoratorMetadata: true
  },
  meta: {
    'typescript': {
      "exports": "ts"
    }
  },  
  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/common/http': 'npm:@angular/common@' + ver.ng + '/bundles/common-http.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.ng + '/bundles/router.umd.js',
    '@angular/forms': 'npm:@angular/forms@' + ver.ng + '/bundles/forms.umd.js',

    'rxjs': 'npm:rxjs@^5.5.2',
    'rxjs/operators': 'npm:rxjs@^5.5.2/operators/index.js',
    'tslib': 'npm:tslib/tslib.js',
    'typescript': 'npm:typescript@2.4.2/lib/typescript.js',

    '@ng-bootstrap/ng-bootstrap': 'npm:@ng-bootstrap/ng-bootstrap@1.0.0-beta.8/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 } from '@angular/forms';
import { HttpClientModule } from '@angular/common/http';
import { NgbModule } from '@ng-bootstrap/ng-bootstrap';
import { BasicComponent } from './basicComponent';

@Component({
  selector: 'my-app',
  template: `
    <div class="container-fluid">
    
    <hr>
    <p>
      This is a demo plnkr forked from the <strong>ng-bootstrap</strong> project: Angular powered Bootstrap.
      Visit <a href="https://ng-bootstrap.github.io/" target="_blank">https://ng-bootstrap.github.io</a> for more widgets and demos.
    </p>
    <hr>

    <basic></basic>
  </div>
  `
})
export class App {
}   

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

import {Component, Directive} from '@angular/core';
import {NgControl} from '@angular/forms';
import {NgbTooltip} from '@ng-bootstrap/ng-bootstrap';

@Component({
  selector: 'basic',
  templateUrl: 'src/basicComponent.html'
})
export class BasicComponent {
    num: string;
    isDisabled = () =>{
      return true;
    };
    
    // generateNewValue=()=>{
    //   this.num = Math.random();
    // }
    
    getTooltipText = () =>{
      if(this.isDisabled()) {
      return "I 'm a tooltip."
      } else{
        return '';
      }
    }
}

Link may be disabled dynamically. 
User on hovering informing why?
<br>
<br>
<div [ngStyle]="{'background': '#ddd'}"
  (click)="generateNewValue()"
  [ngbTooltip]="isDisabled()?'I am Disabled':''"  #t="ngbTooltip">
  asdkaodjad
  asd
  Adad
  asd
  ad
  a
  D
  aSD
  asD
</div>


      
<br>

<div [ngStyle]="{'background': '#ddd'}"
  [ngbTooltip]="getTooltipText()"  #u="ngbTooltip">
  asdkaodjad
  asd
  Adad
  asd
  ad
 
</div>