Building a Simple Store in Angular

Building a Simple Store in Angular

Building a Simple Store in Angular. In this article, we have seen how to create a simple NGXS store from scratch.This is a small example of what can be achieved with a state management library.

One of the biggest challenges I have to face when creating an app is making sure it will not crash in the case of the internet dropping out.

This can be achieved mainly by reducing API calls to the minimum thanks to some kind of local app storage. In these cases, it’s important to have a place where all the main settings and data are kept.

This part of the app, called Store, acts as a single source of truth and allows us to be independent of API calls and have a better data flow between components.

In this article, we will build a simple Store with my favorite state management library for Angular, NGXS. I will link to the full code for the example at the end of the article.

Step 1. Installing the Packages

To have all the necessary modules to create a store, we need to install the packages:

npm i @ngxs/store --save
npm i @ngxs/devtools-plugin --save-dev

packages-install.txt

npm scripts to install NGXS packages

The first package to install is the essential NGXS store library, but I consider the second one fundamental for developing.

As we will see later, thedevtools-plugin, together with the Redux DevTools Extension, will allow us to debug the store in real-time from the browser.

We can then include the downloaded NGXS modules in our app module, specifying that we are injecting them as a singleton in the application root:

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

import { AppRoutingModule } from './app-routing.module';
import { AppComponent } from './app.component';

import { NgxsModule } from '@ngxs/store';
import { NgxsReduxDevtoolsPluginModule } from '@ngxs/devtools-plugin';

@NgModule({
  declarations: [AppComponent],
  imports: [
    BrowserModule,
    AppRoutingModule,
    NgxsModule.forRoot([]),
    NgxsReduxDevtoolsPluginModule.forRoot()
  ],
  providers: [],
  bootstrap: [AppComponent]
})
export class AppModule {}

app.module.ts

Injecting the NGXS modules in app.module

Step 2. Creating a List State

The state we are about to create will store a simple to-do list. We will be able to add a new element as well as delete old ones.

We will begin defining a model for our ListState, in which we’ll declare that the state must have two properties: an array of items representing our to-do list and a variable storing the last element we added to the list.

Moreover, we will define a default set of values with which the state will be initialized. In this case, we will use an empty array for the list and null as value for the last item added:

import { State } from '@ngxs/store';

export interface ListStateModel {
  list: string[];
  lastAdded: string;
}

@State<ListStateModel>({
  name: 'ListState',
  defaults: {
    list: [],
    lastAdded: null
  }
})
export class ListState {}

list.state.ts

ListStateModel and defaults.

We can now activate the newly created state by adding it to the NgXsModule.forRoot method in the imports of app.module:

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

import { AppComponent } from './app.component';

import { NgxsModule } from '@ngxs/store';
import { NgxsReduxDevtoolsPluginModule } from '@ngxs/devtools-plugin';
import { BrowserAnimationsModule } from '@angular/platform-browser/animations';
import { ListContainerComponent } from './components/list-container/list-container.component';
import { MaterialUiModule } from './utils/material-ui/material-ui.module';
import { FormsModule, ReactiveFormsModule } from '@angular/forms';
import { ListItemInputComponent } from './components/list-item-input/list-item-input.component';
import { ListComponent } from './components/list/list.component';
import { ListState } from './store/list.state';
import { AppRoutingModule } from './app-routing.module';

@NgModule({
  declarations: [
    AppComponent,
    ListContainerComponent,
    ListItemInputComponent,
    ListComponent
  ],
  imports: [
    BrowserModule,
    MaterialUiModule,
    BrowserAnimationsModule,
    AppRoutingModule,
    FormsModule,
    ReactiveFormsModule,
    NgxsModule.forRoot([ListState]),
    NgxsReduxDevtoolsPluginModule.forRoot(),
  ],
  providers: [],
  bootstrap: [AppComponent]
})
export class AppModule {}

app.module.ts

State injection

If we serve the app and then open the Redux DevTools extension, we should be able to see that the initial state of the app has been set to our default values.

Moreover, the column on the left will log a message every time an action is dispatched to the store, that is, every time we ask the store to update the values it contains.

In this case, the message @@INIT tells us that the state has been successfully initialized.


Redux DevTools Extension in Chrome

Step 3. Adding Actions to Update the State

At this point, we need to work on the methods that will allow us to edit our to-do list by changing our state.

We can start by creating a list.actions.ts file in which we will define the message we’ll see when a specific action is dispatched and also the type of payload it will take. The action’s payload is simply the data we want to use to edit the state.

export class AddListItem {
  static readonly type = '[List] Add List Item';
  constructor(public readonly payload: string) {}
}
export class DeleteListItem {
  static readonly type = '[List] Delete List Item';
  constructor(public readonly payload: string) {}
}

list.actions.ts

In this case, the action AddListItem will have as payload a string containing the new item to be added to the list. In the same way, DeleteListItem will have as payload a string containing the item to be deleted.

The next step is declaring the methods linked to the actions in list.tate.ts. The method addListItem will get the current state and then add the payload to the list array.

The method removeListItemwill get the current state and filter listto create a new array without the item to be deleted.

import { State, Selector, Action, StateContext } from '@ngxs/store';
import { AddListItem, DeleteListItem } from './list.actions';

export interface ListStateModel {
  list: string[];
  lastAdded: string;
}

@State<ListStateModel>({
  name: 'ListState',
  defaults: {
    list: [],
    lastAdded: null
  }
})
export class ListState {
  @Selector() static SelectAllItems(state: ListStateModel): string[] {
    return state.list;
  }

  @Action(AddListItem)
  addListItem(
    { getState, setState }: StateContext<ListStateModel>,
    { payload }: AddListItem
  ) {
    const state = getState();
    setState({
      list: [...state.list, payload],
      lastAdded: payload
    });
  }

  @Action(DeleteListItem)
  deleteListItem(
    { getState, setState }: StateContext<ListStateModel>,
    { payload }: DeleteListItem
  ) {
    const state = getState();
    console.log('st', state.list);
    const newList = this.arrayRemove(state.list, payload);
    console.log('nl', newList);
    setState({
      ...state,
      list: newList
    });
  }

  private arrayRemove(arr, value) {
    return arr.filter(ele => {
      return ele !== value;
    });
  }
}

list.state.ts

Methods for the Actions declared below

We also declared a method called SelectAllItems, a state selector that allows us to subscribe to listfrom anywhere in our app_._

Step 4. Dispatching an Action

At this point, everything is ready to use the state. In my example, I have set an input field on the landing page to type my new to-do. I also have an “Add Item” button and a “View List” button that will route to the list view.

Input field on the landing page

In the list-input.component, to use the state, we need to initialize it in the constructor. Then, we can call the store’s method dispatch to dispatch an action:

import { Component, OnInit, Input, Output, EventEmitter } from '@angular/core';
import { FormControl, FormGroup } from '@angular/forms';
import { Store } from '@ngxs/store';
import { Router } from '@angular/router';
import { AddListItem } from 'src/app/store/list.actions';

@Component({
  selector: 'app-list-item-input',
  templateUrl: './list-item-input.component.html',
  styleUrls: ['./list-item-input.component.scss']
})
export class ListItemInputComponent implements OnInit {
  form: any;
  showItemAdded = false;

  constructor(private store: Store, private router: Router) {
    this.form = new FormGroup({
      listItem: new FormControl('')
    });
  }

  ngOnInit() {}

  submitItem() {
    this.showItemAdded = true;
    const item = this.form.get('listItem').value;
    this.store.dispatch(new AddListItem(item));
    this.form.reset();
    setTimeout(() => {
      this.showItemAdded = false;
    }, 2000);
  }

  viewList() {
    this.router.navigate(['list']);
  }
}

list-item-input.component.ts

Dispatching an action from the list-input.component

We can also watch the store update using the Redux DevTools. In fact, if we type Buy Bread into the input field and click on Add Item, we will see the item being added to our to-do list in the store when the [List] Add List Itemaction is dispatched.

The dispatched action in the Redux DevTools

Step 5. Reading Values From the State

NGXS makes it also easy to read values from the store from any component in our application.

Let’s suppose we have added three or four to-dos to our list and we want to finally visualize it in another route. We can instantiate the state and use a Selectstatement to get an observable of our list.

Without subscribing to the observable, we can simply read its value through the asyncpipe in our HTML.

<section>
  <mat-card>
    <mat-card-title>Your To-Do List</mat-card-title>
    <mat-card-subtitle>Click on an item to delete it</mat-card-subtitle>
    <app-list
      [listItems]="listItems | async"
      (deleteItemEmt)="deleteItem($event)"
    ></app-list>
  </mat-card>
</section>

list.component.html

import { Component, OnInit } from '@angular/core';
import { FormGroup, FormControl } from '@angular/forms';
import { Store, Select } from '@ngxs/store';
import { ListState } from 'src/app/store/list.state';
import { Observable } from 'rxjs';
import { DeleteListItem } from 'src/app/store/list.actions';

@Component({
  selector: 'app-list-container',
  templateUrl: './list-container.component.html',
  styleUrls: ['./list-container.component.scss']
})
export class ListContainerComponent implements OnInit {
  @Select(ListState.SelectAllItems) listItems: Observable<string[]>;

  constructor(private store: Store) {}
  ngOnInit() {}

  deleteItem(evt: string) {
    console.log(evt);
    this.store.dispatch(new DeleteListItem(evt));
  }
}

list.component.ts

Selecting the list as an observable from the store
Once rendered, we’ll be able to see and interact with our list grabbed from the store:


Async pipe magic!

Conclusion

In this article, we have seen how to create a simple NGXS store from scratch.

This is a small example of what can be achieved with a state management library. There is obviously so much more you can do with NGXS to improve your apps and I would suggest you have a look at the official documentation for some amazing tips and tricks!

Also, check my NGXS demo repo on GitHub to have this code work on your PC!

Hope it is useful!

Migrating from AngularJS to Angular

Migrating from AngularJS to Angular

Migrating from AngularJS to Angular a hybrid system architecture running both AngularJS and Angular

Intro

Dealing with legacy code/technologies is never fun and the path to migration isn’t always as straight forward as you want. If you are a small startup, trying to balance business requirements, scarce resources and aggressive deadlines, it becomes even more complicated.

This is the situation one of the startups I was advising was facing.

A bit of background

The startup was developing a SaaS for the last 2 years and (at the time) had around 15 clients worldwide. In these 2 years their code base grew pretty fast and lead to quite a lot of fast/reckless written code. There was nobody to be blame, this is pretty common in the startup world when business needs move way faster than you expect and you start sacrificing code qualify for quantity.

The system architecture was pretty simple. 
• a frontend application written in AngularJS (split into multiple modules that were selected at build time depending on the clients’ configuration)
• a backend application written in Python 2.7 and Django 1.9 using a Mysql database
• Celery for running async tasks

Each client would get their own isolated environment deployed on AWS:
• Apache in front of the Django application (deployed on multiple EC2 instances behind an ELB)
• AngularJS build deployed on individual S3 buckets with CloudFront in front of them

Path to migration

A few months before starting the migration, development was getting very slow, features were not coming out as fast, deadlines were missed and clients were reporting more issues with every update that we were rolling out. It was at this time that we started thinking more seriously about some kind of refactoring or major improvement.

We didn’t know exactly what we were going to “refactor/improve” so we started off by answering three questions (I recommend that anyone who is thinking about a migration/refactoring think really hard about the how to answer them):

1st question: Why is refactoring necessary now ?

This is a very important questions to answer because it helps you understand the value of the migration and also it helps to keep the team focused on the desired outcome. For example because i don’t like the way the code is written isn’t good enough reason. The reason has to have a clear value proposition that somehow directly or indirectly benefits the customers.

For us it was mainly three things:
 1. feature development was becoming painfully slow;
 2. code was unpredictable. we would work in one part of the application and break 3 other parts without realizing;
 3. single point of failure: only 1 engineer knew the FE code base completely and only he could develop new features on the codebase (this is out of a team of only 5 engineers)

So our goal was simple:

improve FE development velocity and remove the simple point of failure by empowering other engineers to develop FE features

2nd question: Who is going to do the migration ?

You can answer this question either now or after the 3rd question. Depending on the size of the company and on the available resources it can be one person, several people, an entire team, etc…

We were in a difficult situation. The only developer who could work on this couldn’t because he was busy building critical features for our customers. Luckily we had one senior backend engineer who wanted to get some FE exposure so he volunteered to take on the task. We also decided to time-box a proof of concept at 2 weeks. We did this because we didn’t know how long it would take to figure out a solution or whether the engineer could actually do this task since he hadn’t worked on FE before.

3rd question: What are we actually going to do ? The answer here usually involves some discovery time, a few tech proposals and a general overview of the options with the entire team while weighing the pros and cons of each.

For us one thing was clear from the start: we didn’t want to invest any resources into learning/on-boarding engineers on AngularJS. AngularJS had already entered Long Term Support and we didn’t want to have our engineers invest time in something that might not benefit them long term. This meant that refactoring the existing AngularJS code was not an option. So we started looking at Angular6 …

The migration

There a multiple approaches on how to have a hybrid app running different frameworks. After reviewing some options we decided that — for us — the best way to move forward was to simply have 2 separate FE applications deployed: the legacy AngularJS one and the new Angular one. This meant that any state on one app could not be transferred to the other application, which wasn’t such a big deal for us since only new modules were going to be developed using Angular and our modules didn’t share state with each other.

From the client’s perspective everything would look like one application, except for a page reload when they would move between the applications.

Pros to this approach

  • speed: get something up and running without untangling legacy code
  • safety: no risk of breaking the current live app since it would be a new code based deployed next to the old one (especially since a developer with no previous exposure to the project was working on it)
  • stop legacy development: we stop adding more code the an already unmanageable codebase

Cons to this approach:

  • maintaining legacy code: it didn’t address feature improvements on existing modules; old modules would still be in AngularJS for an undefined period of time
  • duplicating parts of the code: since the new app had to look and feel like the old one any themes, custom components would have to be written in both places. Also some parts of the layout would have to be duplicated in new app (like header, menu, etc.. ) and any changes to those components would have to be done in both apps

We already knew of a new module that we wanted to build so we started form scratch with a new Angular 6 project and we used this new module for our 2 weeks proof of concept.

Step 1— same domain

Have both apps running on the same domain so that they have access to the same cookies and local data. This was extremely important since only the AngularJS app would continue handing authentication & authorization.

Step 2— look and feel

Both apps The goal was to make the new app look the same as the original application. So we: 
 • copied over all the stylesheets
 • implemented the base layout of the application (header & menu drawer)

Step 3 — authentication & authorization

We had to duplicate the authorization logic in the Angular6 app and make sure the correct session tokens were available to allow access to the module

Step 4— routing between apps

Since our main navigation links would take you to either app, we decided do move all that logic to a backend service called menu-service. This would eliminate the need to write any navigation changes in both apps and also would allow for greater runtime control over what navigation buttons we show.

Example:

HEADER: Authorization: Bearer xxxxx
GET menu-service/v1/menu/?type=0|1 (0: legacy, 1: new)
[{
  "slug": "refresh",
  "name" : "Refresh",
  "icon" : "fa-refresh",
  "type" : 1  
 }, {
  "slug": "module1",
  "name" : "Module1",
  "icon" : "fa-module1",
  "type" : 1
}, {
  "slug": "module2",
  "name" : "Module2",
  "icon" : "fa-module2",
  "type" : 0
}, {
  "slug": "logout",
  "name" : "Logout",
  "icon" : "fa-logout",
  "type" : 0
}]

In the above example based on the type value we identify that the module1 and refresh are links towards the new application while module2 and logout are links in the old application.
This information allows each application to decide whether to use the internal routing mechanism or do a window.location redirect

Example of routing in the Angular app (AngularJS does something similar):

export class MenuService {
  constructor(private router: Router) {  }
  onMenuItemClicked(menuItem): void {
    if (menuItem.type === 1) {
      this.router.navigate([menuItem.slug])    
    } else {   
      const url = `${legacy_endpoint}/${menuItem.slug}`;
      window.location.href = url      
    } 
  }
}

Step 5— building/deployment on a real environment

Like i mentioned in the beginning the AngularJS application was deployed to an AWS S3 bucket and exposed through Cloudfront to take advantage of the massively scaled and globally distributed infrastructure offered by AWS.

The result we wanted was the following: anything that has the url [https://hostname/v2](https://hostname/v2)/ is routed to the Angular application and everything else is routed to the legacy AngularJS app.

We used base-href and to make sure our Angular6 application builds accordingly

ng build --base-href /v2/ --deploy-url /v2/

Unfortunately we didn’t manage to achieve the desired routing behavior with AWS Cloudfront. This was a big disappointment since we had to pivot to a less optimal solution. (if anyone has any suggestion on how to do this in Cloudfront i’d love to hear it)

We ended up with the following structure:
• each app deployed in a NGINX Docker container

# AngularJS — Dockerfile:
FROM nginx:alpine
COPY dist /usr/share/nginx/html
--------------------------------------------------------------------
# Angular6 — Dockerfile:
FROM nginx:alpine
COPY dist /usr/share/nginx/html/v2

• AWS ALB with path routing

Step 6: Local development

Local development for the AngularJS application didn’t have to change. However in order to develop on the Angular6 app you had to also run the AngularJS application to be able to authenticate and get the appropriate session tokens.

We were already using Docker for deploying our application as containers. So we added a Makefile target to run the latest from our Docker repository

# Angular6 — Makefile:
AWS_REPOSITORY = xxx.dkr.ecr.eu-central-1.amazonaws.com
JS_APP_NAME = angular-js
...
run-local: 
  docker run -p 8080:80 $(AWS_REPOSITORY)/$(JS_APP_NAME):latest

Conclusion

This might not be the cleanest or optimal solution, however it was the fastest way towards our goals. And this was the most important thing to us.

The goal of this post isn’t to teach you how to do a AngularJS to Angular6 migration but instead is to showcase our path when dealing with such a task.

Further reading:

An in-depth look at Angular’s ng template

Angular 8 Data (Event & Property) Binding Tutorial: Build your First Angular App

Angular 8 Forms Tutorial - Reactive Forms Validation Example

What is the difference between JavaScript and AngularJS?

JavaScript is a client-side programming language used for creating dynamic websites and apps to run in the client's browser whereas AngularJS is a fully featured web app framework established on JavaScript and managed by Google.

JavaScript is a client-side programming language used for creating dynamic websites and apps to run in the client's browser whereas AngularJS is a fully featured web app framework established on JavaScript and managed by Google.


What’s the difference between AngularJS and Angular?

What’s the difference between AngularJS and Angular?

Angular vs Angularjs - key differences, performance, and popularity

AngularJS was released in 2009 and quickly became popular for it's two-way data binding, MVC architecture, and code reusability.

When alternatives like React and Vue delivered the same advantages of AngularJS with better performance, the Angular team decided to completely rewrite the framework.

Each subsequent release of Angular (4,5,6,7,8) has been mostly non-breaking incremental changes. For these reasons, "Angular" now refers to Angular 2+ and "AngularJS" the original.

Key Differences

Here are the key differences between Angular 2+ and AngularJS:

TypeScript

Angular was rewritten using TypeScript. TypeScript is a superset of JavaScript. It compiles to regular vanilla JavaScript but provides syntax for type checking, annotations, and ES6 based extensions.

Since TypeScript is a superset of JavaScript, it needs to be compiled or "transpiled" into ES5 JavaScript so your code still runs in the browser. This requires the use of NodeJS and other build tools for preprocessing TypeScript files.

While using Angular 2+ without TypeScript is possible, the industry standard is to adopt TypeScript as it plays much better with the Angular ecosystem.

MVC vs Component Architecture

AngularJS adheres to the model, view, controller (MVC) software design pattern. Controllers are defined with $scope variables representing an underlying data model. This data model can be updated in both the view and the controller. The view is an HTML file which both displays and dynamically updates $scope variables.

Angular 2+ utilizes more of a component based architecture. Isolated pieces of functionality are defined in components. These components reference their own templates and stylesheets and exist in a hierarchy of other components.

Dependency Injection (DI)

Both AngularJS and Angular use dependency injection. DI allows you to share commonly used functionality across different controllers or components.

In AngularJS, dependencies are injected in controller functions, link functions, and directive definitions.

In Angular, constructor functions, providers, and declarations are used to manage these dependencies.

Angular CLI

Angular 2+ features the Angular CLI: a command line interface for quickly generating Angular components, services, directives, etc. It comes with convenient commands for building your Angular project (compiling TypeScript files and other assets into vanilla js files that run in the browser). It also makes building your project for different environments easier and allows for things like linting, type checking, etc.

AngularJS doesn't have it's own CLI.

Performance

Angular is much faster than AngularJS. In fact, it's said that Angular can be more than 5X faster based on the design of your application.

Popularity

Before the advent of React and Vue, AngularJS was very popular. It offered an elegant solution to the JavaScript SPA with two-way data binding and MVC architecture.

Being able to dynamically update a JavaScript POJO from an HTML template caused a lot of buzz. As a result, alternatives like React and Vue emerged with superior diffing algorithms that left AngularJS in the dust.

Angular fought back with the release of Angular 2 (2016). Today, Angular remains one of the most popular frameworks for UI development.

While AngularJS is still used today, it's popularity has died in favor of more current options like Angular 2+, React, and Vue.

Performance

The problem with AngularJS

Performance is one of the biggest problems with the original AngularJS. This is due to the underlying "magic" behind what originally made AngularJS so popular.

To achieve two-way data binding, AngularJS relies on a digest cycle to keep views in sync with their underlying data models. It works by augmenting all event handlers (clicks, ajax, timeouts) with a process called "dirty checking". Each scoped variable is compared to it's previous value.

If something has changed, the watchers and templates are updated with the new value and the process runs again to see if anything else has changed. In this way, the view is constantly in sync with the data model.

The problem with the AngularJS digest cycle is it's unpredictable. As applications grow, the "checking" process becomes more intensive and can run infinitely with two way data flow.

Angular 2+ to the rescue

To address these issues, the Angular team rewrote the framework with flux architecture in mind. Specifically unidirectional data flow was fundamental to reengineering change detection in Angular.

Now the Angular framework is just as fast as alternatives. When compared to AngularJS, Angular can be more than 5X faster.

The Angular CLI also makes minifying production bundle sizes a breeze, keeping Angular light weight for production.

Advantages of Angular

Angular offers many advantages over the original AngularJS:

Performance:

Angular is up to 5X faster than AngularJS. This is because of a superior diffing algorithm featuring unidirectional data flow and component based architecture.

Server side rendering

Angular offers extensions for rendering your application server side. This is huge for SEO as certain web crawlers can't always scrape async content.

Mobile development

As a framework, Angular makes it possible to develop applications that work on both browsers and native devices like iOS and Android.

Lazy loading

Lazy loading allows you to asynchronously load JavaScript components based on route. This can offer additional performance advantages as code is only imported when it's being used.

Tooling

The tooling provided by TypeScript and the NodeJS ecosystem can't be underestimated. Using the Angular CLI, you can quickly generate Angular components, services, directives etc. without having to manually copy / paste a bunch of boilerplate code.

Additionally, you can more easily build and deploy your project using the CLI.

Should I use Angular or AngularJS?

With the performance advantages, Angular may seem like the best bet moving forward. There is a substantial learning curve to understanding the NodeJS / TypeScript ecosystem and one of the few advantages of AngularJS is that it just runs in the browser.

Using AngularJS makes sense if you have a small application and don't want to bother with learning the ins and outs of NodeJS and TypeScript.

There are also many existing projects out there that already use AngularJS and migrating to newer versions may not justify the cost of learning and rewriting code.

Outside of these cases, adopting "Angular" over the original "AngularJS" is preferred moving forward.

Thanks for reading

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Further reading about Angular

Angular 8 (formerly Angular 2) - The Complete Guide

Angular & NodeJS - The MEAN Stack Guide

The Complete Node.js Developer Course (3rd Edition)

The Web Developer Bootcamp

Best 50 Angular Interview Questions for Frontend Developers in 2019

How to build a CRUD Web App with Angular 8.0

React vs Angular: An In-depth Comparison

React vs Angular vs Vue.js by Example

Microfrontends — Connecting JavaScript frameworks together (React, Angular, Vue etc)

Building CRUD Mobile App using Ionic 4, Angular 8

How to Build Mobile Apps with Angular, Ionic 4, and Spring Boot

Ionic 4 & Angular Tutorial For Beginners - Crash Course