How to configure bootstrap 4 in Angular

Below are the steps I have done for configuring the Bootstrap 4 in Angular 7.

Tested In Angular 7.0.0

Step 1 – Install the required dependencies

 npm install bootstrap (if you want specific version please specify the version no.)

npm install popper.js (if you want specific version please specify the version no.)

npm install jquery

Versions I have tried:

"bootstrap": "^4.1.3",
"popper.js": "^1.14.5",
"jquery": "^3.3.1",

Step 2 : Specify the libraries in below order in angular.json. In latest angular , the config file name is angular.json not angular-cli.json

"architect": {
"build": {
"builder": "@angular-devkit/build-angular:browser",
"options": {
"outputPath": "dist/client",
"index": "src/index.html",
"main": "src/main.ts",
"polyfills": "src/polyfills.ts",
"tsConfig": "src/",
"assets": [
"styles": [
"scripts": [


How to copy JSON files in to your dist folder without create all directory

Version : Webpack 4

You can use copy-webpack-plugin to copy files or directory from your source directory to dist folder.

For example  I am going to copy all JSON files from inside the app folder to dist/assets/ folder



if you didn’t specify flatten = true , all the directory will create in dist folder like below

Introduction to Service worker

Service Workers  are like a JavaScript files , but they have access to set of features and also it’s run on a separate thread. It will not share the thread where the normal JavaScript code loaded by your html pages runs on. When you register a service worker through your  html page or code initially , it will manage all the pages of a given scope. For example if your service worker is attached to the root of your application , then it’s applicable to all the html pages not only the single html page.

Service worker is also live on even after you closed all the pages in the browser .For example if you are using a mobile phone, even if you close the application , service worker will run as a background process.

What we can do with service workers?

Since it’s background process ,service workers can react all kind of incoming events from your JavaScript code as well as from your server as web push notification and can do something based on that , for example you can return a cached asset , show some notifications to the user and so on.

Type of events which service workers can listen to


By using fetch API you can initiate an http request asynchronously to get some resources across the network. This new API is similar to XmlHttpRequest , but  provides a more powerful and flexible feature set

.then(function(response) {
return response.json();


What you can do with this fetch API in service worker?

By using service worker every http request send via fetch API can intercept like a network proxy.So you can block the request if you want and also you can manipulate the request.

self.addEventListener('fetch', function (event) {



Also  the image tags which point to some image resource in the html will also send a fetch request by the browser. So you can cache the same by intercepting it.

Push Notifications

Every browser like Google Chrome,Mozilla Firefox has its own web push  server , So you can push notifications from your web server to this web push server and then browser will send this notifications to your client. This feature is very useful for a mobile to receive push notifications even if we are not in the application.

How to Register a service worker?

Please note one thing  , the scope of the service worker depends on the location of the file. If the file is  on your root of the application , service workers are applies to all pages in your application. If you can create the file in sub folder , service worker could only control the pages inside of this folder.

  • Create a new file , you can give any name you want . Here I gave sw.js
  • Add your service worker registration code , you can add this in to your start up js file.
if ('serviceWorker' in navigator) {
   .then(function () {
       console.log('Service worker registered!');
   .catch(function(err) {

That’s it .

How Observable works in RxJS?

What is Observable?

Observable is a like a stream which allow to pass zero or more events or values  and you can subscribe each using a callback function.

Why Observables are so important?

In almost all UI when user do some interactions with it you can see the same progression. for example

  • You are listening an event
  • You are making an asynchronous request to the server and may be you are follow up with some transformations or Animations

Observables are capable of modeling all the above things together with a very little code.

In order to understand how Observable works , look at the sample code

var observable = Observable.create(function(observer) {
var sum = 0;
for (var i = 1; i <= 4; i++) {
if (i <= 3) { sum = sum + i;; //You can emit each item from the observable also } if (i === 4) { setTimeout( i => {;

In this sample code, I am running a for loop and emit each value by using , when the value of i become 4 you can see emiting the sum of 3 numbers and exiting the all observable sequence by simple calling observable.complete();

Observables are lazy which means , the above code never executes unless you are subscribing it.

Let’s subscribe the Observable to get each value. I am removing the lambda expression to understand more clearly

next: function(x) {
console.log("got value " + x);
error: err => console.error("something wrong occurred: " + err),
complete: function() {
//when I become 4 it will complete

In the callback function of next , you will get all the values emitted from the Observable sequence including sum as final value and finally execute the complete callback function.

You can simply receive each value like the below syntax also instead of specify next explicitly

observable.subscribe(function(x) {
//here you will get all the value including sum

Let me tell you one more scenario with the same sample by simply commenting one line of code. I am not emitting each value instead I want to emit the sum only from the observable and complete.

var observable = Observable.create(function(observer) {
var sum = 0;
for (var i = 1; i <= 4; i++) {
if (i <= 3) { sum = sum + i; //commented the code } if (i === 4) { setTimeout( i => {;

Now when you subscribe , you will have only one value , that is sum

observable.subscribe(function(x) {
//here you will the sum

Official Documenation to learn about RxJS features

Introduction to Progressive Web Apps

PWA is not a technology or a framework , set of features in web which helps to improve your application progressively. It means if you have a modern browser you will get an awesome user experience else those features just not support it , your application will have existing features remains as it is.

Let’s talk about what all the features we can use to enhance our existing or new web application .

1. You can bring native look and feel of mobile device apps on your web pages. It’s not the responsiveness of web page but you can access the native features such as camera , accessing geo location, push notifications.
2. Offline Capability when your internet connection get lost.
3. Background Synchronization of data
4. Icon on the home screen , you don’t need to install the application from the app store to place it on your home screen.

There are three import things I want to summarize about the progressive web application.

Reliable : Application will load instantly even in a uncertain condition and provide offline functionality through caching.
Fast : Respond quickly as possible based on the user interactions.

Engaging : Feels like a native app on mobile devices.

Can’t resolve all parameters in Angular and Webpack

I have recently faced an issue while configuring an Angular 6 application using Webpack 4 , All the dependencies I am injecting in to the component are throwing error.

This error will throw because of various reasons such as circular dependency , not properly spelled @Injectable() decorator etc. You can check the scenarios in the below link

My issue was little bit different , typescript is not resolving decorator> To fix the issue I have set emitDecoratorMetadata=true in tsconfig.json file

Load Angular component styleUrl using web pack

The only change you have to make on your component is , instead of providing the url path using styleUrl , import the file using require and convert to string.

To get the require keyword in typescript, you have to install an npm package called ‘@types/node’
npm install @types/node --save-dev

Also if you want to build and load the scss make sure that you have installed sass-loader and style-loader for web pack

npm install sass-loader --save-dev
npm install style-loader --save-dev

Plugins for webpack

npm install mini-css-extract-plugin --save-dev


rules: [{
test: /\.(sa|sc|c)ss$/,
use: [
loader: MiniCssExtractPlugin.loader,

plugins: [

new CleanWebpackPlugin(['dist']),
new MiniCssExtractPlugin({

filename: '[name].styles.css',
chunkFilename: '[name].styles.css'