npm install ngx-read-time --save

import { Component } from '@angular/core';
import { ReadTimeConfig, TimeUnit } from 'ngx-read-time';

@Component({
  selector: 'app-root',
  templateUrl: './app.component.html',
  styleUrls: ['./app.component.css']
})
export class AppComponent {
  title = 'demo';
  readTime: string;
  rtConfig: ReadTimeConfig = {
    wordsPerMinute: 250,
    timeUnit: TimeUnit.MINUTES
  }
}

<article nrtReadTime [options]="rtConfig" (timeCalculated)="readTime = $event.minutes">
    <h1>Understanding Discriminated Unions in Typescript
      <span>
        <a href="https://dev.to/ahsanayaz/understanding-discriminated-unions-in-typescript-5cd">
          (Source)
        </a>
      </span>
    </h1>

    // Here will the description of the article
  </article>

import { BrowserModule } from '@angular/platform-browser';
import { NgModule } from '@angular/core';

import { AppComponent } from './app.component';
import { NgxReadTimeModule } from 'ngx-read-time';

@NgModule({
  declarations: [
    AppComponent
  ],
  imports: [
    BrowserModule,
    NgxReadTimeModule
  ],
  providers: [],
  bootstrap: [AppComponent]
})
export class AppModule { }