Angular

QR Code Scanning & Generation

Dec 13, 2023

4 min read

QR Code Scanning & Generation with ZXing and Angular

QR codes provide a very valuable way of sharing information with users, and many applications rely on them for various purposes. Common examples of places where QR codes can be useful include but are not limited to theaters, social gatherings and other booking services. Integrating QR codes can seem intimidating, but thankfully they’re not too difficult to handle with Angular and the help of a couple of robust software libraries such as ZXing.

What is ZXing?

ZXing, also known as “Zebra Crossing” is a software library that allows developers to easily integrate scanning many different types of 1D and 2D barcodes. This library was originally written in Java, however many ports to other languages and platforms exist, including JavaScript.

There are a couple of ways to use ZXing. You could either directly use the JavaScript library, which is framework-agnostic, or you could use a framework-specific library. I’m going to demonstrate how to use ZXing to scan QR codes with the Angular version of the library called ngx-scanner specifically, which has a full-fledged scanner component that makes it somewhat easy to integrate.

Let’s Scan some QR Codes with Angular!

Getting ngx-scanner up and running doesn’t take much setup at all. All you have to do is add an import to ZXingScannerModule inside of the module that you will be scanning QR codes in, and add a component to your template. Below shows a real-world example of how the <zxing-scanner> component would be used.

<zxing-scanner
  #scanner
  *ngIf="startCamera$ | async"
  class="scanner"
  [enable]="(enable$ | async) ?? false"
  [autostart]="true"
  [device]="(selectedDevice$ | async) ?? undefined"
  [formats]="allowedFormats"
  (camerasFound)="devices$.next($event)"
  (scanSuccess)="scanSuccess$.next($event)"
  (scanError)="scanError($event)"
></zxing-scanner>

You’ll notice a lot of observables being referenced here. I’ll go over them one by one. Let’s start with the devices subject:

devices$ = new BehaviorSubject<MediaDeviceInfo[]>([]);

This subject has data sent to it whenever cameras have been identified by the scanning component. We want to keep track of these so that we’re able to select a camera to use. In our case we’ll just select the first camera for simplicity's sake, as you can see happens with the selectedDevice$ observable that we have bound to the [device] attribute on the scanner:

selectedDevice$: Observable<MediaDeviceInfo> = this.devices$.pipe(
  map((device) => device[0]),
  distinctUntilChanged(),
  shareReplay(1)
);

We utilize shareReplay here so we don’t need to re-scan the devices whenever additional subscribers check what devices are available.

enable$ is a simple observable that emits true whenever devices have been detected, and startCamera$ is an observable that toggles between true and false whenever data is pushed to the toggleCamera$ subject.

toggleCamera$ = new BehaviorSubject<boolean>(false);

startCamera$ = this.toggleCamera$.pipe(
  scan((acc) => !acc, true),
  startWith(true)
);

The scan function from RxJs is utilized so we have the previous state and can use that to determine in which direction the stored boolean should toggle to.

Finally we push successfully scanned codes to scanSuccess$ which we can then subscribe to in the template.

All together the final component code should look something like this:

@Component({
  selector: 'app-scanner',
  templateUrl: './scanner.component.html',
  styleUrls: ['./scanner.component.scss'],
})
export class ScannerComponent {
  @ViewChild('scanner') scanner!: ZXingScannerComponent;

  allowedFormats = [BarcodeFormat.QR_CODE];

  devices$ = new BehaviorSubject<MediaDeviceInfo[]>([]);

  selectedDevice$: Observable<MediaDeviceInfo> = this.devices$.pipe(
    map((device) => device[0]),
    distinctUntilChanged(),
    shareReplay(1)
  );

  enable$ = this.devices$.pipe(map(Boolean));

  toggleCamera$ = new BehaviorSubject<boolean>(false);

  startCamera$ = this.toggleCamera$.pipe(
    scan((acc) => !acc, true),
    startWith(true)
  );

  scanSuccess$ = new BehaviorSubject<string>('');

  scanError(error: Error) {
    console.error(error);
  }
}

If we use this component then you should get something that looks like this: QR code scanning

Scanning QR codes is awesome, but we can also generate our own QR codes as well!

Generating our own QR Codes

Unfortunately the ZXing scanner component we’re using is limited to just scanning QR codes, however there is another component library called ngx-kjua that can do this. Like ZXing this component is also based off of another pre-existing library that is framework-agnostic, in this case, kjua.

Fortunately kjua is very easy to use. You simply supply it a code and it will render a QR code.

<ngx-kjua
  class="code"
  *ngIf="code$ | async"
  [text]="code$ | async"
  [size]="256"
></ngx-kjua>

How the QR code is rendered can change. There is an optional [render] attribute that you can specify that takes a few values. You can input ‘image’, ‘canvas’ or ‘svg’. The default render mode is ‘svg’. It should be noted that ‘svg’ and ‘canvas’ render modes made copying the image more difficult, so use ‘image’ if you want to make that possible.

The component code associated with this template is very small. The component using ngx-kjua has a code observable that is updated with a new random code whenever a “Generate” button is pressed.

import { Component } from '@angular/core';
import { BehaviorSubject } from 'rxjs';
import randomstring from 'randomstring';

@Component({
  selector: 'app-generator',
  templateUrl: './generator.component.html',
  styleUrls: ['./generator.component.scss'],
})
export class GeneratorComponent {
  code$ = new BehaviorSubject<string>(this.generateCode());

  generateCodeClick(event: MouseEvent) {
    this.code$.next(this.generateCode());
  }

  private generateCode(): string {
    return randomstring.generate({ length: 12, charset: 'alphabetic' });
  }
}

I’ve opted to go with the randomstring package in this case. This component could be modified to instead allow for custom codes using a textbox if you want to encode URLs or other useful values that typically go inside of QR codes.

The result looks like this: QR code scanner result

Summary

Thanks to projects like ZXing and kjua it is easy to integrate handling of QR codes in Angular applications, be it for scanning them or creating them. I hope this guide has helped you. You can find the full example showcasing generation and scanning of QR codes in our blog-demos repository on GitHub.

This Dot is a consultancy dedicated to guiding companies through their modernization and digital transformation journeys. Specializing in replatforming, modernizing, and launching new initiatives, we stand out by taking true ownership of your engineering projects.

We love helping teams with projects that have missed their deadlines or helping keep your strategic digital initiatives on course. Check out our case studies and our clients that trust us with their engineering.

Jamie Kuppens

I’m a software engineer with an interest in web development and some more esoteric things like emulator development.

@Reshurum @Reshurum

Using HttpClient in Modern Angular Applications

Introduction With all the wonderful treats that the Angular team has given us during the recent "renaissance" era, many new developers are joining in on the fun. And one of the challenges they'll face at some point is how to call an API from your Angular application properly. Unfortunately, while searching for a guide on how to do this, they might stumble upon a lot of outdated information. Hence, this article should serve as a reliable guide on how to use the HttpClient in Angular >= 17. The Setup To make an HTTP request in Angular, you can take advantage of the HttpClient provided by the @angular/common/http package. To use it, you'll need to provide it. Here's how you can do that for the whole application using the bootstrapApplication function from @angular/platform-browser: ` With that, you should be good to go. You can now inject the HttpClient into any service or component in your application. Using HttpClient in Services Let's take a common example: You have a database object, say a Movie, and you want to implement CRUD operations on it. Typically, you'll want to create a service that provides methods for these operations. Let's call this service MovieService and create a skeleton for it with a method for getting all movies. ` Implementing the Method using HttpClient Let's assume we have a GraphQL API for our movies. We can implement our getAllMovies using HttpClient to make a request to fetch all movies. First, we will need to define a new type to represent the response from the API. This is especially important when you are using GraphQL, which may return a specific structure, such as: ` When working with a real API, you'll likely use some code generator to generate the types for the response from the GraphQL schema. But for the sake of this example, we'll create an interface to represent the response manually: ` Now, we can implement the getAllMovies method using HttpClient: ` > Note: The post method is used here because we are sending a request body. If you are making a GET request (e.g. to a REST API), you can use the get method instead. The getAllMovies method returns an Observable of MoviesListResponse. In this example, I have typed it explicitly to make it obvious at first glance, but you could also omit the type annotation, and TypeScript should infer it. > Note: While I'm excited about signals as much as the next guy, making HTTP requests is one of the typical async operations for which RxJS Observables are a perfect fit, making a great argument for RxJS still having a solid place in Angular alongside signals. Using the Service in a Component Now that we have our MovieService set up, we can use it as a component to fetch and display all movies. But first, let's create a Movie interface to represent the structure of a movie. Trust me, this will prevent many potential headaches down the line. Although using any at the beginning and implementing the types later is a valid approach in some cases, using data fetched from an API without validating the type will inevitably lead to bugs that are difficult to solve. ` Now, we can start implementing our standalone MoviesComponent: ` In this component, we are calling the getAllMovies method from the MovieService in the constructor to fetch all movies and assign them to the movies property which we will use to display the movies in the template. ` In this case, placing our code inside the constructor is safe because it doesn’t depend on any @Input(). If it were, our code would fail because the inputs aren’t initialized at time of instantiation. That's why it is sometimes recommended to place logic in ngOnInit instead. You could also put this call in an arbitrary method that is called e.g. on a button click. Another way to handle the subscription is to use the async pipe in the template. This way, Angular will automatically subscribe and unsubscribe from the observable for you and you won't have to assign the response to a property in the component. Due to the structure of the returned data, however, we'll need to use the RxJS map operator to extract the movies from the response. ` > Note using the pipe method to chain the map operator to the observable returned by getAllMovies. This is a common pattern when working with RxJS observables introduced in RxJs 5.5. If you see code that uses the map operator directly on the observable and wonder why it isn't working for you, it's likely using an older version of RxJS. Now, we can simply apply the async pipe in the template to subscribe to the observable and display the movies: ` Conclusion HttpClient in Angular is pretty straightforward, but with all the changes to RxJS and Angular in the past few years, it can pose a significant challenge if you're not super-experienced with those technologies and stumble upon outdated resources. Following this article, you should hopefully be able to implement your service using HttpClient to make requests to an API in your modern Angular application and avoid the struggle of copying outdated code snippets....

Mar 27, 2024

4 mins

AngularJavaScript

4 Angular Component Libraries That are Perfect for Beginners

For beginners starting with Angular, the journey can feel daunting, especially when it comes to setting up projects from scratch. However, there is a range of outstanding Angular component libraries that alleviate this initial hurdle: ready-made toolkits, empowering newcomers to start building Angular applications without the complexities of bootstrapping their projects. Let’s take a look! Angular Material Angular Material is a UI component library by Google for Angular applications. It provides a variety of pre-built components following the Material Design guidelines, offering customization options, responsive design, and accessibility features. It's seamlessly integrated with Angular and offers extensive documentation and community support. NG-ZORRO NG-ZORRO is an Angular UI component library based on Ant Design by Alibaba. It offers a variety of customizable components for building modern web applications. With seamless Angular integration, responsive design, and accessibility features, NG-ZORRO simplifies development while following Ant Design principles. NG Bootstrap NG Bootstrap is a library for Angular developers to easily incorporate Bootstrap components into their applications without relying on jQuery. It offers Angular-specific directives and components, ensuring compatibility and performance within Angular projects while maintaining Bootstrap's responsive design and customization options. Clarity Design System Clarity is an open-source design system by VMware that offers a set of Angular components for building enterprise-scale applications. It provides components specifically tailored for data-centric applications, dashboards, and complex user interfaces. Clarity Design System emphasizes clarity, consistency, and usability in its components. The beginner’s journey can be both exhilarating and challenging. However, with the advent of powerful component libraries like Angular Material, NG-ZORRO, NG Bootstrap, and the Clarity Design System, the path becomes significantly smoother. These libraries offer pre-built components and design systems that eliminate the need to bootstrap projects from scratch. As beginners embark on their Angular journey, these libraries provide a sturdy foundation, allowing them to dive into development with confidence. By harnessing the capabilities of these libraries, beginners can not only expedite their learning curve but also craft exceptional Angular applications with ease and efficiency....

Mar 14, 2024

2 mins

Angular

CSS Hooks: A new way to style your React apps

In the world of web development, the management of styles has always been a crucial aspect of building modern and responsive user interfaces. With the rise of CSS in JS libraries like Material UI and Chakra, developers have started creating dynamic and reusable styles using JavaScript; however, the performance implications of these libraries have led to the exploration of alternative solutions. One such solution is CSS Hooks, a library that offers a different approach to managing styles in web applications. The Problem with CSS in React and CSS in JS Libraries In React applications, you typically write styles directly with the style prop by applying classes with className, or if you’re using a framework like Material UI or Chakra then you may use the sx attribute, which is more powerful than the baseline attributes. There are some performance concerns in the case of the sx attribute specifically. The framework has to dynamically generate classes with your styles and apply them to the document whenever it is used. This can become an issue with large and complex applications as your styles will be regularly regenerated on the fly as the user navigates through the application. This has led developers to seek alternative solutions that offer similar flexibility but with better performance. Introduction to CSS Hooks CSS Hooks improve upon the aforementioned issues by pre-generating your CSS using configuration hooks. The styles that these hooks generate remain static during the lifetime of the application and are reused wherever possible. CSS variables are utilized under the hood whenever dynamic behavior is needed. By dynamic behavior, I’m referring to advanced CSS features such as pseudo-class selectors and media queries, which are both traditionally unavailable for use with inline styles. CSS Hooks utilize an interesting trick under the hood to accomplish this, which we will now explore. The Power of CSS Variables and the Fallback Trick As mentioned before, CSS variables are utilized in order to support using advanced dynamic behavior such as pseudo-selectors in our inline styles. CSS variables are core to something known as the “fallback trick”. The gist of how the fallback trick works is to have the pseudo-selector or media query toggle the state of a variable between initial and an empty invalid value, and then we put the value that we actually want to toggle as the “fallback” value in the reference to the CSS variable inside of the inline style itself. Changing this fallback value inside of an inline style essentially allows us to control the values used by the pseudo-selector without having to regenerate linked stylesheets as we only have to change the inline style attribute. This is best explained with an example: ` This plain HTML and CSS code effectively allows us to utilize the focus pseudo-selector on any element that we want using inline styles only. This is what CSS Hooks effectively does in the background when you use dynamic styles. No nasty re-renders and mucking with stylesheets needed! How to use CSS Hooks Now that we know how CSS Hooks fundamentally work, let’s try using them. The library itself is much easier to use than the aforementioned example. Installation and usage of CSS Hooks is easy. Firstly, we must install the @css-hooks/react package into a React project with the package manager of your choice (npm, pnpm yarn, etc). Once that’s done, all that’s left is a little bit of configuration. You have to first use a utility function called createHooks that is exported from the package we just installed. The result of that function returns a couple of variables in an array that can be deconstructed, the first being a stylesheet in the form of a string, and the second being a function. ` I recommend putting this in a separate file that can be imported from multiple other places in the project as this is where we will be configuring hooks across the project. We’re exporting both hooks and css, and both are important. We need to include hooks into the DOM as it contains the styles of the hooks that we’ll be referencing in our components. In your root component you need to add the following tag so that the generated CSS can be used. ` How this is done may vary based on the libraries that you are using. After that’s done, you can integrate CSS Hooks into your components while writing inline styles mostly just like you would do normally, with the only change being the addition of an additional call to the css function that we exported earlier: ` Now that the core boilerplate is set up, your components can now utilize CSS Hooks in theory; however we need to actually add some hooks to start with before we can use them, or else we’ll just be limited to basic styles in the same way that React inline styles are. Make your own hooks We can define our hooks inside of the css-hooks file that we created earlier, the same one that exports the css helper function that gets CSS Hooks working with our components. Hooks are defined in the options parameters that are currently empty. Defining a simple hook that allows us to define inline hover styles for a component is very easy and can be done as follows: ` Although both the key and the value in this example are the same, they both serve different purposes. The key is the name of the hook that we reference when we want to use it, while the value is the spec. The spec is the actual CSS selector that we’re writing. The name can be anything that you want it to be so long as it doesn’t clash with any existing style properties or hooks. Recommended hooks Although making your own hooks may be necessary at times, there is another repository provided by the CSS Hooks authors that adds a way to generate many useful hooks called @css-hooks/recommended. I highly recommend using this library to generate your hooks if at all possible, and the usage is pretty simple. Here’s an example showing how you can use it to generate media queries, color scheme specific styles and pseudo-selectors: ` Then with that done, these can be utilized as follows: ` We can also modify the hooks configuration to add our own hooks in addition to the recommended hooks by using the spread operator: ` Then that custom hook can be used by simply using its key name: ` Summary CSS Hooks offers a performant alternative to traditional CSS in JS libraries by leveraging CSS variables and providing a unique approach to managing styles in web applications. By pre-generating the stylesheet based on configured hooks and utilizing CSS Variables for dynamic behavior, developers can create reusable styles without the performance overhead associated with dynamic stylesheet generation. If you're interested in exploring CSS Hooks further, be sure to check out @CSSHooks for more information. You can also find some of the examples demonstrated here in a working app in our demos repository. Thank you for reading!...

Feb 28, 2024

5 mins

CSSReact

How to Make Coding Both Your Hobby and Profession with Jason Lengsdorf @ CityJS Conf 2024

Join us backstage at CityJS Conf for this conversation with Jason Lengsdorf. In this discussion, we explore strategies for reducing stress and anxiety among engineers, ensuring they maintain relevance in the dynamic world of coding. Jason emphasizes the importance of self-assurance and the role of play in fostering continual engagement with evolving technologies. Moreover, we get a sneak peek into Jason's latest venture, "Web Lunch," a platform where he converses with developers who have found harmony between their careers and personal satisfaction. Coding isn't just a job; it's a passion and a lifestyle. Jason highlights the significance of pursuing work that excites and challenges us, echoing the sentiment that coding can be both a career and a hobby. By infusing enjoyment and creativity into our coding endeavors, we can shape our professional trajectories in alignment with our values and interests. This approach not only minimizes regret but also maximizes happiness and fulfillment in our careers. Central to our discussion is the pivotal role of effective leadership in creating a supportive and encouraging work environment. Leaders who prioritize the well-being and happiness of their team members foster a culture of collaboration and empowerment. Through mentorship, guidance, and opportunities for growth, these leaders enable developers to align their personal goals with organizational objectives, leading to increased job satisfaction and professional fulfillment. Adaptability is key to sustained success in software engineering. Jason emphasizes the value of remaining open-minded and continuously learning, even when it means stepping out of our comfort zones. Embracing discomfort is an integral part of personal growth, allowing us to overcome obstacles and unlock our full potential. By nurturing a spirit of curiosity and adaptability, developers can navigate the complexities of their careers with resilience and enthusiasm....

Apr 25, 2024

2 mins

JavaScriptMentorship

QR Code Scanning & Generation

QR Code Scanning & Generation with ZXing and Angular

What is ZXing?

Let’s Scan some QR Codes with Angular!

Generating our own QR Codes

Summary

Jamie Kuppens

You might also like

Using HttpClient in Modern Angular Applications

4 Angular Component Libraries That are Perfect for Beginners

CSS Hooks: A new way to style your React apps

How to Make Coding Both Your Hobby and Profession with Jason Lengsdorf @ CityJS Conf 2024

You might also like

Using HttpClient in Modern Angular Applications

4 Angular Component Libraries That are Perfect for Beginners

CSS Hooks: A new way to style your React apps

How to Make Coding Both Your Hobby and Profession with Jason Lengsdorf @ CityJS Conf 2024