Angular

Migrating AngularJS to Angular

Published Jan 13, 2021

Updated Feb 16, 2023

8 min read

This article was written over 18 months ago and may contain information that is out of date. Some content may be relevant but please refer to the relevant official documentation or available resources for the latest information.

Introduction

There is still a lot of confusion around Angular and AngularJS. It has gotten better, but searching for "Angular" still provides ambiguous results.

This is a problem because AngularJS is on Long Term Support (LTS) mode. It entered LTS on July 1, 2018, for 3 years. It was granted a six-month extension due to COVID-19. Therefore, all support is expected to end on December 31, 2021, meaning Google will stop fixing bugs and providing support for AngularJS.

All Angular engineering effort will be focused on the latest version of Angular making it prudent that active AngularJS codebases are migrated to Angular this year.

This article will showcase different migration paths available to achieve this.

Big Bang Rewrite

By far, the easiest way to migrate a legacy codebase is to simply start fresh from the ground up. You won't have to worry about conflicting packages or supporting different versions of the same package.

You would simply use the latest Angular CLI to scaffold out a new app and begin working on re-implementing your legacy app features with Angular.

However, this is a significant engineering effort.

This approach is excellent for very small AngularJS apps. However, it can also be possible for larger codebases.

For larger codebases, you could set aside one or two developers to perform bug fixes and tackle production issues on the AngularJS app. You would inform customers that new features will be considered but will likely take some time to become available in the app. You would then concentrate the rest of your engineering effort on rewriting the app in Angular.

This allows you to support your current app as it stands whilst reaching feature parity with the new Angular version of the app.

UpgradeModule

UpgradeModule is a tool provided by ngUpgrade by Angular to aid in the migration process. It allows you to run a hybrid application, mixing Angular and AngularJS apps. There is no emulation; it runs both frameworks at the same time.

UpgradeModule provides us with two options on how we run our application. We can either run the AngularJS app and downgrade our Angular code into it, or we can run the Angular app and upgrade our AngularJS code into Angular.

The Angular docs provide incredible documentation on setting up the hybrid application (you can read more here). We'll cover the basics here.

Downgrading to run in AngularJS

Generally, AngularJS apps can be bootstrapped using the ng-app directive such as:

<body ng-app="myApp">
</body>

However, for ngUpgrade to take full effect you need to manually bootstrap AngularJS:

angular.bootstrap(document.body, ['myApp'], {strictDi: true});

The next step in running the latest Angular framework in the AngularJS context is to load the framework itself.

This involves an outdated setup process where we need to use SystemJS to set up our Angular framework. The Angular framework no longer uses SystemJS by default for loading the framework; however, they have written a guide on how to do this here.

We then set up Angular to provide it with a reference to the AngularJS App and more importantly, its Dependency Injector: $injector.

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

@NgModule({
  imports: [
    BrowserModule,
    UpgradeModule
  ]
})
export class AppModule {
  constructor(private upgrade: UpgradeModule) { }
  ngDoBootstrap() {
    this.upgrade.bootstrap(document.body, ['myApp'], { strictDi: true });
  }
}

Notice that this.upgrade.bootstrap has the same signature as angular.bootstrap.

The final thing to do now is to bootstrap the Angular framework, which is done easily with one line:

platformBrowserDynamic().bootstrapModule(AppModule);

Now we can create new Angular components and downgrade them into AngularJS.

Say we have an Angular component called HelloComponent. We use downgradeComponent provided by ngUpgrade to allow this component to be available to use in the AngularJS app:

import { downgradeComponent } from '@angular/upgrade/static';
import { HelloComponent } from './hello.component';

angular.module('myApp', [])
  .directive(
    'helloWorld',
    downgradeComponent({ component: HelloComponent }) as angular.IDirectiveFactory
  );

We can then use this in an AngularJS template:

<div ng-controller="MainCtrl as ctrl">
    <hello-world></hello-world>
</div>

Notice that the directive is registered in camelCase (helloWorld) but we use it in our HTML with kebab-case (hello-world).

You're all set up to start migrating your components to Angular and downgrading them to be used in AngularJS.

However, I like to think you'll agree that there is a lot of setting up here, and it leaves you with an Angular codebase that uses SystemJS to bootstrap and load your app.

Upgrading to run in Angular

We can take a different approach with ngUpgrade and UpgradeModule, however. We could lazy load our AngularJS app into an Angular app that was scaffolded by the Angular CLI getting the full benefit of the build tools and leaving us with a codebase in line with the latest Angular.

The Angular docs provide a great guide on setting up the Lazy Load Approach.

It involves four things:

An Angular Service to lazy load AngularJS and bootstrap the AngularJS App
A file providing an entry point for AngularJS and the AngularJS App
An Angular Component to render the AngularJS app (a wrapper component)
Telling the Angular router when to route within the AngularJS app

Once these are complete (the Angular docs really do explain this best), you can start creating new Angular components and downgrading them to be used in the AngularJS app similarly to how it was done in the previous section.

You also get the benefit of a more straightforward method to upgrade AngularJS services to be used within Angular:

You create a factory provider and add it to the providers array of your Angular Module:

export function myServiceFactory(i: any) {
  return i.get('my');
}

export const myServiceProvider = {
  provide: myService,
  useFactory: myServiceFactory,
  deps: ['$injector']
};

/* ... */

@NgModule({
    declarations: [MyComponent],
    providers: [myServiceProvider]
})
export class MyModule {}

This means you can focus on upgrading your AngularJS components first, then circling back to your services afterwards.

This approach allows you to use all the modern Angular tools as well as providing you with an option of splitting up your AngularJS into smaller modules and only loading them as required. It also allows you to focus on upgrading smaller chunks of the AngularJS app at a time.

Take a look at this folder structure for an example:

You would store the relevant AngularJS code for the feature in the corresponding angularjs folder. This means your team can focus on one feature at a time without losing any functionality for your customers.

Angular Elements

Another approach that is gaining some popularity is to use Angular's Web Component solution, called Angular Elements.

Angular Elements allows you to package up your Angular Component as a Web Component enabling it to be distributed and rendered in a plain old JavaScript context.

This is awesome for migrating AngularJS codebases. It means we can create an Angular Component, bundle it as a Web Component and drop it into our AngularJS codebase with less set up than the ngUpgrade approach.

This approach does have some drawbacks. We need a good build pipeline that will bundle the Angular Components, make them available, and include them into the AngularJS codebase so that they can be loaded and used in this context.

One approach to take that employs this would be to create two folders: one for your AngularJS codebase, one for your Angular codebase.

You would keep your AngularJS codebase as is. All new work would occur in the Angular codebase.

You can use the Angular CLI to scaffold out a monorepo. Each component you intend to upgrade would live in its own /projects folder (this is an Angular CLI workspace convention).

To do this, you can run the command:

ng generate application my-component

Next, you need to add Angular Elements to your workspace:

ng add @angular/elements --project=my-component

This would create a folder and accompanying files at /projects/my-component.

You would then create your component:

ng generate component my-component --project=my-component

This will scaffold out the component files you need.

Once you have finished setting up your component, you need to use Angular Elements to convert it to a Web Component.

Modify the app.module.ts at the root of /projects/my-component:

@NgModule({
    imports: [BrowserModule],
    declarations: [MyComponent],
    bootstrap: [],
    entryComponents: [MyComponent]
})
export class AppModule {
    constructor(private injector: Injector) {
        const myComponent = createCustomElement(MyComponent, {
            injector
        });
        customElements.define('my-component', myComponent);
    }

    ngDoBootstrap() {}
}

When we build our app, we need to copy the output into a public folder in our AngularJS codebase.

To build the elements file:

ng build --prod --project=my-component

This will produce output similar to:

Notice that it created 4 files: 3 JavaScript files and one CSS file. They contain hashes to allow for cache-busting. However, it would also be worth bundling these together and naming them related to the component.

We can do this with a simple node.js script (concat-elements-bundle.js):

const fs = require('fs');

const pathToComponent = './dist/my-component';

const javascriptFiles = fs.readdirSync(pathToComponent).filter(file => file.endsWith(".js"));

let fileData;
for(const file of javascriptFiles) {
  fileData += fs.readFileSync(`${pathToComponent}/${file}`);
}

const hash = Date.now();
fs.writeFileSync(`./dist/my-component/my-component.bundle.${hash}.js`, fileData)

We can run this on the command line using node:

node concat-elements-bundle.js

This will output something similar to:

my-component.bundle.1610106946217.js

We then need to copy this to a scripts folder in our AngularJS and include it using a script tag in our index.html file:

<script type="text/javascript" src="app/scripts/my-component.bundle.1610106946217.js"></script>

We can then use our component anywhere in our AngularJS app:

<div ng-controller="MyCtrl as ctrl">
    <my-component></my-component>
</div>

This approach allows us to incrementally upgrade components to Angular, using Angular's modern tooling without changing our existing app's set up much. Once all components are upgraded, we have to place the components together in an Angular app, completing the migration.

With a good CI Pipeline we _could _ automate the bundling and inclusion of the Angular Element in the AngularJS app, requiring even less work as the migration moves forward.

Best Practice for Upgrading

No matter the approach taken, one thing remains consistent between the two of them: how we tackle the migration.

Consider our application to be a tree of components. The closer to the root of the tree, the more complex and usually more coupled the components are. As we move down the nodes in the tree, the components should get simpler and be coupled with fewer components.

These components, the lowest hanging fruits, are ideal candidates for migrating to Angular first. We can migrate these components then use them in the AngularJS app where appropriate.

Let's say we have an AngularJS TodoList Component which uses an AngularJS Todo Component.

At this point, we can't really migrate the TodoList Component to Angular as we would have a dependency on the AngularJS Todo Component.

We can migrate the Todo Component to Angular first and use it in the TodoList Component. This makes it easier to migrate the TodoList Component as its dependency on the Todo Component is already an Angular Component.

We can use this approach when migrating legacy codebases. Start from the bottom and work our way up, and I would say this is the best approach.

Conclusion

With AngularJS losing support at the end of this year, it's worthwhile looking at migrating any legacy AngularJS codebases as soon as possible and figuring out a plan to do so.

Hopefully, this article has illustrated the different options available for you to do this and helped provide an approach to tackling migrating the components in your codebase.

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.

About the author(s)

Colum Ferry
JavaScript Developer and Enthusiast. Really enjoy working with Angular. Married with 2 amazing kids. Powered by Coffee.
@FerryColum @https://github.com/coly010

Exploring Angular Forms: A New Alternative with Signals

Exploring Angular Forms: A New Alternative with Signals In the world of Angular, forms are essential for user interaction, whether you're crafting a simple login page or a more complex user profile interface. Angular traditionally offers two primary approaches: template-driven forms and reactive forms. In my previous series on Angular Reactive Forms, I explored how to harness reactive forms' power to manage complex logic, create dynamic forms, and build custom form controls. A new tool for managing reactivity - signals - has been introduced in version 16 of Angular and has been the focus of Angular maintainers ever since, becoming stable with version 17. Signals allow you to handle state changes declaratively, offering an exciting alternative that combines the simplicity of template-driven forms with the robust reactivity of reactive forms. This article will examine how signals can add reactivity to both simple and complex forms in Angular. Recap: Angular Forms Approaches Before diving into the topic of enhancing template-driven forms with signals, let’s quickly recap Angular's traditional forms approaches: 1. Template-Driven Forms: Defined directly in the HTML template using directives like ngModel, these forms are easy to set up and are ideal for simple forms. However, they may not provide the fine-grained control required for more complex scenarios. Here's a minimal example of a template-driven form: ` ` 2. Reactive Forms: Managed programmatically in the component class using Angular's FormGroup, FormControl, and FormArray classes; reactive forms offer granular control over form state and validation. This approach is well-suited for complex forms, as my previous articles on Angular Reactive Forms discussed. And here's a minimal example of a reactive form: ` ` Introducing Signals as a New Way to Handle Form Reactivity With the release of Angular 16, signals have emerged as a new way to manage reactivity. Signals provide a declarative approach to state management, making your code more predictable and easier to understand. When applied to forms, signals can enhance the simplicity of template-driven forms while offering the reactivity and control typically associated with reactive forms. Let’s explore how signals can be used in both simple and complex form scenarios. Example 1: A Simple Template-Driven Form with Signals Consider a basic login form. Typically, this would be implemented using template-driven forms like this: ` ` This approach works well for simple forms, but by introducing signals, we can keep the simplicity while adding reactive capabilities: ` ` In this example, the form fields are defined as signals, allowing for reactive updates whenever the form state changes. The formValue signal provides a computed value that reflects the current state of the form. This approach offers a more declarative way to manage form state and reactivity, combining the simplicity of template-driven forms with the power of signals. You may be tempted to define the form directly as an object inside a signal. While such an approach may seem more concise, typing into the individual fields does not dispatch reactivity updates, which is usually a deal breaker. Here’s an example StackBlitz with a component suffering from such an issue: Therefore, if you'd like to react to changes in the form fields, it's better to define each field as a separate signal. By defining each form field as a separate signal, you ensure that changes to individual fields trigger reactivity updates correctly. Example 2: A Complex Form with Signals You may see little benefit in using signals for simple forms like the login form above, but they truly shine when handling more complex forms. Let's explore a more intricate scenario - a user profile form that includes fields like firstName, lastName, email, phoneNumbers, and address. The phoneNumbers field is dynamic, allowing users to add or remove phone numbers as needed. Here's how this form might be defined using signals: ` > Notice that the phoneNumbers field is defined as a signal of an array of signals. This structure allows us to track changes to individual phone numbers and update the form state reactively. The addPhoneNumber and removePhoneNumber methods update the phoneNumbers signal array, triggering reactivity updates in the form. ` > In the template, we use the phoneNumbers signal array to dynamically render the phone number input fields. The addPhoneNumber and removePhoneNumber methods allow users to reactively add or remove phone numbers, updating the form state. Notice the usage of the track function, which is necessary to ensure that the ngFor directive tracks changes to the phoneNumbers array correctly. Here's a StackBlitz demo of the complex form example for you to play around with: Validating Forms with Signals Validation is critical to any form, ensuring that user input meets the required criteria before submission. With signals, validation can be handled in a reactive and declarative manner. In the complex form example above, we've implemented a computed signal called formValid, which checks whether all fields meet specific validation criteria. The validation logic can easily be customized to accommodate different rules, such as checking for valid email formats or ensuring that all required fields are filled out. Using signals for validation allows you to create more maintainable and testable code, as the validation rules are clearly defined and react automatically to changes in form fields. It can even be abstracted into a separate utility to make it reusable across different forms. In the complex form example, the formValid signal ensures that all required fields are filled and validates the email and phone numbers format. This approach to validation is a bit simple and needs to be better connected to the actual form fields. While it will work for many use cases, in some cases, you might want to wait until explicit "signal forms" support is added to Angular. Tim Deschryver started implementing some abstractions around signal forms, including validation and wrote an article about it. Let's see if something like this will be added to Angular in the future. Why Use Signals in Angular Forms? The adoption of signals in Angular provides a powerful new way to manage form state and reactivity. Signals offer a flexible, declarative approach that can simplify complex form handling by combining the strengths of template-driven forms and reactive forms. Here are some key benefits of using signals in Angular forms: 1. Declarative State Management: Signals allow you to define form fields and computed values declaratively, making your code more predictable and easier to understand. 2. Reactivity: Signals provide reactive updates to form fields, ensuring that changes to the form state trigger reactivity updates automatically. 3. Granular Control: Signals allow you to define form fields at a granular level, enabling fine-grained control over form state and validation. 4. Dynamic Forms: Signals can be used to create dynamic forms with fields that can be added or removed dynamically, providing a flexible way to handle complex form scenarios. 5. Simplicity: Signals can offer a simpler, more concise way to manage form states than traditional reactive forms, making building and maintaining complex forms easier. Conclusion In my previous articles, we explored the powerful features of Angular reactive forms, from dynamic form construction to custom form controls. With the introduction of signals, Angular developers have a new tool that merges the simplicity of template-driven forms with the reactivity of reactive forms. While many use cases warrant Reactive Forms, signals provide a fresh, powerful alternative for managing form state in Angular applications requiring a more straightforward, declarative approach. As Angular continues to evolve, experimenting with these new features will help you build more maintainable, performant applications. Happy coding!...

Oct 4, 2024

5 mins

AngularJavaScript

How to build an AI assistant with OpenAI, Vercel AI SDK, and Ollama with Next.js

In today’s blog post, we’ll build an AI Assistant using three different AI models: Whisper and TTS from OpenAI and Llama 3.1 from Meta. While exploring AI, I wanted to try different things and create an AI assistant that works by voice. This curiosity led me to combine OpenAI’s Whisper and TTS models with Meta’s Llama 3.1 to build a voice-activated assistant. Here’s how these models will work together: * First, we’ll send our audio to the Whisper model, which will convert it from speech to text. * Next, we’ll pass that text to the Llama 3.1 model. Llama will understand the text and generate a response. * Finally, we’ll take Llama’s response and send it to the TTS model, turning the text back into speech. We’ll then stream that audio back to the client. Let’s dive in and start building this excellent AI Assistant! Getting started We will use different tools to build our assistant. To build our client side, we will use Next.js. However, you could choose whichever framework you prefer. To use our OpenAI models, we will use their TypeScript / JavaScript SDK. To use this API, we require the following environmental variable: OPENAI_API_KEY— To get this key, we need to log in to the OpenAI dashboard and find the API keys section. Here, we can generate a new key. Awesome. Now, to use our Llama 3.1 model, we will use Ollama and the Vercel AI SDK, utilizing a provider called ollama-ai-provider. Ollama will allow us to download our preferred model (we could even use a different one, like Phi) and run it locally. The Vercel SDK will facilitate its use in our Next.js project. To use Ollama, we just need to download it and choose our preferred model. For this blog post, we are going to select Llama 3.1. After installing Ollama, we can verify if it is working by opening our terminal and writing the following command: Notice that I wrote “llama3.1” because that’s my chosen model, but you should use the one you downloaded. Kicking things off It's time to kick things off by setting up our Next.js app. Let's start with this command: ` After running the command, you’ll see a few prompts to set the app's details. Let's go step by step: * Name your app. * Enable app router. The other steps are optional and entirely up to you. In my case, I also chose to use TypeScript and Tailwind CSS. Now that’s done, let’s go into our project and install the dependencies that we need to run our models: ` Building our client logic Now, our goal is to record our voice, send it to the backend, and then receive a voice response from it. To record our audio, we need to use client-side functions, which means we need to use client components. In our case, we don’t want to transform our whole page to use client capabilities and have the whole tree in the client bundle; instead, we would prefer to use Server components and import our client components to progressively enhance our application. So, let’s create a separate component that will handle the client-side logic. Inside our app folder, let's create a components folder, and here, we will be creating our component: ` Let’s go ahead and initialize our component. I went ahead and added a button with some styles in it: ` And then import it into our Page Server component: ` Now, if we run our app, we should see the following: Awesome! Now, our button doesn’t do anything, but our goal is to record our audio and send it to someplace; for that, let us create a hook that will contain our logic: ` We will use two APIs to record our voice: navigator and MediaRecorder. The navigator API will give us information about the user’s media devices like the user media audio, and the MediaRecorder will help us record the audio from it. This is how they’re going to play out together: ` Let’s explain this code step by step. First, we create two new states. The first one is for keeping track of when we are recording, and the second one stores the instance of our MediaRecorder. ` Then, we’ll create our first method, startRecording. Here, we are going to have the logic to start recording our audio. We first check if the user has media devices available thanks to the navigator API that gives us information about the browser environment of our user: If we don’t have media devices to record our audio, we just return. If they do, then let us create a stream using their audio media device. ` Finally, we go ahead and create an instance of a MediaRecorder to record this audio: ` Then we need a method to stop our recording, which will be our stopRecording. Here, we will just stop our recording in case a media recorder exists. ` We are recording our audio, but we are not storing it anywhere. Let’s add a new useEffect and ref to accomplish this. We would need a new ref, and this is where our chunks of audio data will be stored. ` In our useEffect we are going to do two main things: store those chunks in our ref, and when it stops, we are going to create a new Blob of type audio/mp3: ` It is time to wire this hook with our AudioRecorder component: ` Let’s go to the other side of the coin, the backend! Setting up our Server side We want to use our models on the server to keep things safe and run faster. Let’s create a new route and add a handler for it using route handlers from Next.js. In our App folder, let’s make an “Api” folder with the following route in it: We want to use our models on the server to keep things safe and run faster. Let’s create a new route and add a handler for it using route handlers from Next.js. In our App folder, let’s make an “Api” folder with the following route in it: ` Our route is called ‘chat’. In the route.ts file, we’ll set up our handler. Let’s start by setting up our OpenAI SDK. ` In this route, we’ll send the audio from the front end as a base64 string. Then, we’ll receive it and turn it into a Buffer object. ` It’s time to use our first model. We want to turn this audio into text and use OpenAI’s Whisper Speech-To-Text model. Whisper needs an audio file to create the text. Since we have a Buffer instead of a file, we’ll use their ‘toFile’ method to convert our audio Buffer into an audio file like this: ` Notice that we specified “mp3”. This is one of the many extensions that the Whisper model can use. You can see the full list of supported extensions here: https://platform.openai.com/docs/api-reference/audio/createTranscription#audio-createtranscription-file Now that our file is ready, let’s pass it to Whisper! Using our OpenAI instance, this is how we will invoke our model: ` That’s it! Now, we can move on to the next step: using Llama 3.1 to interpret this text and give us an answer. We’ll use two methods for this. First, we’ll use ‘ollama’ from the ‘ollama-ai-provider’ package, which lets us use this model with our locally running Ollama. Then, we’ll use ‘generateText’ from the Vercel AI SDK to generate the text. Side note: To make our Ollama run locally, we need to write the following command in the terminal: ` ` Finally, we have our last model: TTS from OpenAI. We want to reply to our user with audio, so this model will be really helpful. It will turn our text into speech: ` The TTS model will turn our response into an audio file. We want to stream this audio back to the user like this: ` And that’s all the whole backend code! Now, back to the frontend to finish wiring everything up. Putting It All Together In our useRecordVoice.tsx hook, let's create a new method that will call our API endpoint. This method will also take the response back and play to the user the audio that we are streaming from the backend. ` Great! Now that we’re getting our streamed response, we need to handle it and play the audio back to the user. We’ll use the AudioContext API for this. This API allows us to store the audio, decode it and play it to the user once it’s ready: ` And that's it! Now the user should hear the audio response on their device. To wrap things up, let's make our app a bit nicer by adding a little loading indicator: ` Conclusion In this blog post, we saw how combining multiple AI models can help us achieve our goals. We learned to run AI models like Llama 3.1 locally and use them in our Next.js app. We also discovered how to send audio to these models and stream back a response, playing the audio back to the user. This is just one of many ways you can use AI—the possibilities are endless. AI models are amazing tools that let us create things that were once hard to achieve with such quality. Thanks for reading; now, it’s your turn to build something amazing with AI! You can find the complete demo on GitHub: AI Assistant with Whisper TTS and Ollama using Next.js...

Sep 27, 2024

8 mins

AINextJSJavaScript

Best Practices for Managing RxJS Subscriptions

When we use RxJS, it's standard practice to subscribe to Observables. By doing so, we create a Subscription. This object provides us with some methods that will aid in managing these subscriptions. This is very important, and is something that should not be overlooked! Why do we care about subscription management? If we do not put some thought into how we manage and clean up the subscriptions we create, we can cause an array of problems in our applications. This is due to how the Observer Pattern is implemented. When an Observable emits a new value, its Observers execute code that was set up during the subscription. For example: ` If we do not manage this subscription, every time obs$ emits a new value doSomethingWithDataReceived will be called. Let's say this code is set up on the Home View of our App. It should only ever be run when the user is on the Home View. Without managing this subscription correctly when the user navigates to a new view in the App, doSomethingWithDataReceived could still be called, potentially causing unexpected results, errors or even hard-to-track bugs. So what do we mean by Subscription Management? Essentially, subscription management revolves around knowing when to complete or unsubscribe from an Observable, to prevent incorrect code from being executed, especially when we would not expect it to be executed. We can refer to this management of subscriptions as cleaning up active subscriptions. How can we clean up subscriptions? So, now that we know that managing subscriptions are an essential part of working with RxJS, what methods are available for us to manage them? Unsubscribing Manually One method we can use, is to unsubscribe manually from active subscriptions when we no longer require them. RxJS provides us with a convenient method to do this. It lives on the Subscription object and is simply called .unsubscribe(). If we take the example we had above; we can see how easy it is to unsubscribe when we need to: ` 1. We create a variable to store the subscription. 2. We store the subscription in a variable when we enter the view. 3. We unsubscribe from the subscription when we leave the view preventing doSomethingWithDataReceived() from being executed when we don't need it. This is great; however, when working with RxJS, you will likely have more than one subscription. Calling unsubscribe for each of them could get tedious. A solution I have seen many codebases employ is to store an array of active subscriptions, loop through this array, unsubscribing from each when required. Let's modify the example above to see how we could do this: ` 1. We create an array to store the subscriptions. 2. We add each subscription to the array when we enter the view. 3. We loop through and unsubscribe from the subscriptions in the array. These are both valid methods of managing subscriptions and can and should be employed when necessary. There are other options however, that can add a bit more resilience to your management of subscriptions. Using Operators RxJS provides us with some operators that will clean up the subscription automatically when a condition is met, meaning we do not need to worry about setting up a variable to track our subscriptions. Let's take a look at some of these! first The first operator will take only the first value emitted, or the first value that meets the specified criteria. Then it will complete, meaning we do not have to worry about manually unsubscribing. Let's see how we would use this with our example above: ` When obs$ emits a value, first() will pass the value to doSomethingWithDataReceived and then unsubscribe! take The take operator allows us to specify how many values we want to receive from the Observable before we unsubscribe. This means that when we receive the specified number of values, take will automatically unsubscribe! ` Once obs$ has emitted five values, take will unsubscribe automatically! takeUntil The takeUntil operator provides us with an option to continue to receive values from an Observable until a different, notifier Observable emits a new value. Let's see it in action: ` 1. We create a notifier$ Observable using a Subject. _(You can learn more about Creating Observables here.)_ 2. We use takeUntil to state that we want to receive values until notifier$ emits a value 3. We tell notifier$ to emit a value and complete _(we need to clean notifer$ up ourselves) when we leave the view, allowing our original subscription to be unsubscribed. takeWhile Another option is the takeWhile operator. It allows us to continue receiving values whilst a specified condition remains true. Once it becomes false, it will unsubscribe automatically. ` In the example above we can see that whilst the property finished on the data emitted is false we will continue to receive values. When it turns to true, takeWhile will unsubscribe! BONUS: With Angular RxJS and Angular go hand-in-hand, even if the Angular team has tried to make the framework as agnostic as possible. From this, we usually find ourselves having to manage subscriptions in some manner. async Pipe Angular itself provides one option for us to manage subscriptions, the async pipe. This pipe will subscribe to an Observable in the template, and when the template is destroyed, it will unsubscribe from the Observable automatically. It's very simple to use: ` By using the as data, we set the value emitted from the Observable to a template variable called data, allowing us to use it elsewhere in the children nodes to the div node. When the template is destroyed, Angular will handle the cleanup! untilDestroyed Another option comes from a third-party library developed by Netanel Basal. It's called until-destroyed, and it provides us with multiple options for cleaning up subscriptions in Angular when Angular destroys a Component. We can use it similarly to takeUntil: ` It can _also_ find which properties in your component are Subscription objects and automatically unsubscribe from them: ` This little library can be beneficial for managing subscriptions for Angular! When should we employ one of these methods? The simple answer to this question would be: > When we no longer want to execute code when the Observable emits a new value But that doesn't give an example use-case. - We have covered one example use case in this article: when you navigate away from a view in your SPA. - In Angular, you'd want to use it when you destroy Components. - Combined with State Management, you could use it only to select a slice of state once that you do not expect to change over the lifecycle of the application. - Generally, you'd want to do it when a condition is met. This condition could be anything from the first click a user makes to when a certain length of time has passed. Next time you're working with RxJS and subscriptions, think about when you no longer want to receive values from an Observable, and ensure you have code that will allow this to happen!...

Dec 14, 2020

5 mins

RxJSJavaScriptAngular

Introduction to Zod for Data Validation

As web developers, we're often working with data from external sources like APIs we don't control or user inputs submitted to our backends. We can't always rely on this data to take the form we expect, and we can encounter unexpected errors when it deviates from expectations. But with the Zod library, we can define what our data ought to look like and parse the incoming data against those defined schemas. This lets us work with that data confidently, or to quickly throw an error when it isn't correct. Why use Zod? TypeScript is great for letting us define the shape of our data in our code. It helps us write more correct code the first time around by warning us if we are doing something we shouldn't. But TypeScript can't do everything for us. For example, we can define a variable as a string or a number, but we can't say "a string that starts with user_id_ and is 20 characters long" or "an integer between 1 and 5". There are limits to how much TypeScript can narrow down our data for us. Also, TypeScript is a tool for us developers. When we compile our code, our types are not available to the vanilla JavaScript. JavaScript can't validate that the data we actually use in our code matches what we thought we'd get when we wrote our TypeScript types unless you're willing to manually write code to perform those checks. This is where we can reach for a tool like Zod. With Zod, we can write data schemas. These schemas, in the simplest scenarios, look very much like TypeScript types. But we can do more with Zod than we can with TypeScript alone. Zod schemas let us create additional rules for data parsing and validation. A 20-character string that starts with user_id_? It's z.string().startsWith('user_id_').length(20). An integer between 1 and 5 inclusive? It's z.number().int().gte(1).lte(5). Zod's primitives give us many extra functions to be more specific about *exactly* what data we expect. Unlike TypeScript, Zod schemas aren't removed on compilation to JavaScript—we still have access to them! If our app receives some data, we can verify that it matches the expected shape by passing it to your Zod schema's parse function. You'll either get back your data in exactly the shape you defined in your schema, or Zod will give you an error to tell you what was wrong. Zod schemas aren't a replacement for TypeScript; rather, they are an excellent complement. Once we've defined our Zod schema, it's simple to derive a TypeScript type from it and to use that type as we normally would. But when we really need to be sure our data conforms to the schema, we can always parse the data with our schema for that extra confidence. Defining Data Schemas Zod schemas are the variables that define our expectations for the shape of our data, validate those expectations, and transform the data if necessary to match our desired shape. It's easy to start with simple schemas, and to add complexity as required. Zod provides different functions that represent data structures and related validation options, which can be combined to create larger schemas. In many cases, you'll probably be building a schema for a data object with properties of some primitive type. For example, here's a schema that would validate a JavaScript object representing an order for a pizza: ` Zod provides a number of primitives for defining schemas that line up with JavaScript primitives: string, number, bigint, boolean, date, symbol, undefined, and null. It also includes primitives void, any, unknown, and never for additional typing information. In addition to basic primitives, Zod can define object, array, and other native data structure schemas, as well as schemas for data structures not natively part of JavaScript like tuple and enum. The documentation contains considerable detail on the available data structures and how to use them. Parsing and Validating Data with Schemas With Zod schemas, you're not only telling your program what data should look like; you're also creating the tools to easily verify that the incoming data matches the schema definitions. This is where Zod really shines, as it greatly simplifies the process of validating data like user inputs or third party API responses. Let's say you're writing a website form to register new users. At a minimum, you'll need to make sure the new user's email address is a valid email address. For a password, we'll ask for something at least 8 characters long and including one letter, one number, and one special character. (Yes, this is not really the best way to write strong passwords; but for the sake of showing off how Zod works, we're going with it.) We'll also ask the user to confirm their password by typing it twice. First, let's create a Zod schema to model these inputs: ` So far, this schema is pretty basic. It's only making sure that whatever the user types as an email is an email, and it's checking that the password is at least 8 characters long. But it is *not* checking if password and confirmPassword match, nor checking for the complexity requirements. Let's enhance our schema to fix that! ` By adding refine with a custom validation function, we have been able to verify that the passwords match. If they don't, parsing will give us an error to let us know that the data was invalid. We can also chain refine functions to add checks for our password complexity rules: ` Here we've chained multiple refine functions. You could alternatively use superRefine, which gives you even more fine grained control. Now that we've built out our schema and added refinements for extra validation, we can parse some user inputs. Let's see two test cases: one that's bound to fail, and one that will succeed. ` There are two main ways we can use our schema to validate our data: parse and safeParse. The main difference is that parse will throw an error if validation fails, while safeParse will return an object with a success property of either true or false, and either a data property with your parsed data or an error property with the details of a ZodError explaining why the parsing failed. In the case of our example data, userInput2 will parse just fine and return the data for you to use. But userInput1 will create a ZodError listing all of the ways it has failed validation. ` ` We can use these error messages to communicate to the user how they need to fix their form inputs if validation fails. Each error in the list describes the validation failure and gives us a human readable message to go with it. You'll notice that the validation errors for checking for a valid email and for checking password length have a lot of details, but we've got three items at the end of the error list that don't really tell us anything useful: just a custom error of Invalid input. The first is from our refine checking if the passwords match, and the second two are from our refine functions checking for password complexity (numbers and special characters). Let's modify our refine functions so that these errors are useful! We'll add our own error parameters to customize the message we get back and the path to the data that failed validation. ` Now, our error messages from failures in refine are informative! You can figure out which form fields aren't validating from the path, and then display the messages next to form fields to let the user know how to remedy the error. ` By giving our refine checks a custom path and message, we can make better use of the returned errors. In this case, we can highlight specific problem form fields for the user and give them the message about what is wrong. Integrating with TypeScript Integrating Zod with TypeScript is very easy. Using z.infer<typeof YourSchema> will allow you to avoid writing extra TypeScript types that merely reflect the intent of your Zod schemas. You can create a type from any Zod schema like so: ` Using a TypeScript type derived from a Zod schema does *not* give you any extra level of data validation at the type level beyond what TypeScript is capable of. If you create a type from z.string.min(3).max(20), the TypeScript type will still just be string. And when compiled to JavaScript, even that will be gone! That's why you still need to use parse/safeParse on incoming data to validate it before proceeding as if it really does match your requirements. A common pattern with inferring types from Zod schemas is to use the same name for both. Because the schema is a variable, there's no name conflict if the type uses the same name. However, I find that this can lead to confusing situations when trying to import one or the other—my personal preference is to name the Zod schema with Schema at the end to make it clear which is which. Conclusion Zod is an excellent tool for easily and confidently asserting that the data you're working with is exactly the sort of data you were expecting. It gives us the ability to assert at runtime that we've got what we wanted, and allows us to then craft strategies to handle what happens if that data is wrong. Combined with the ability to infer TypeScript types from Zod schemas, it lets us write and run more reliable code with greater confidence....

Nov 15, 2024

7 mins

JavaScriptZod

Let's innovate together!

We're ready to be your trusted technical partners in your digital innovation journey.

Whether it's modernization or custom software solutions, our team of experts can guide you through best practices and how to build scalable, performant software that lasts.

Migrating AngularJS to Angular

Introduction

Big Bang Rewrite

UpgradeModule

Downgrading to run in AngularJS

Upgrading to run in Angular

Angular Elements

Best Practice for Upgrading

Conclusion

Colum Ferry

You might also like

Exploring Angular Forms: A New Alternative with Signals

How to build an AI assistant with OpenAI, Vercel AI SDK, and Ollama with Next.js

Best Practices for Managing RxJS Subscriptions

Introduction to Zod for Data Validation

Let's innovate together!

You might also like

Exploring Angular Forms: A New Alternative with Signals

How to build an AI assistant with OpenAI, Vercel AI SDK, and Ollama with Next.js

Best Practices for Managing RxJS Subscriptions

Introduction to Zod for Data Validation