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This article was written over 18 months ago and may contain information that is out of date.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

Making Seamless Page Transitions with the View Transitions API

Make Seamless Page Transitions using the View Transitions API Traditionally web applications have always had a less polished experience, both functionally and visually speaking, compared to native applications on mobile and other platforms. This has been improving over the years with the introduction of new web APIs and standards. One such new API that bridges that gap is the View Transitions API. What is the View Transitions API? The View Transitions API is a new browser feature that allows developers to more easily create animated transitions between pages and views, similar to how mobile apps have transitions when navigating between pages. Adding view transitions to your application can reduce the cognitive load on your users and make the experience feel less inconsistent. One great thing about view transitions is that they can be used by both SPAs (single-page applications) and MPAs (multi-page applications) alike! Using the View Transitions API for SPAs Let’s see how we can use view transitions ourselves. We will use examples adapted from demos created by the wonderful Jake Archibald and Bramus. There are some alterations to a few of the examples to make them work with the newest version of the View Transitions API, but otherwise, they’re mostly the same. The process of getting view transitions working for SPAs is as simple as calling document.startViewTransition right before starting navigation and replacing your page’s content immediately after that. You need to make this call in your router or in an event listener that triggers your page navigation. The following is an example of how you can hook into page navigation in a vanilla JavaScript application. This example uses the Navigation API if it’s available. As of the time of writing this article only Chromium-based browsers support the Navigation API, but there is a fallback to using a click listener on link elements so that this works with Firefox and Safari. ` If you’re using a framework, then there’s probably a better way to do this specific to that framework than by using this contrived example. For example, if you are implementing usage of this API with a Next application, you may opt for something like next-view-transitions. For this article, we’re going to focus on the way this is done in vanilla JavaScript so that the fundamentals of using the API are understood. Knowing how it’s implemented in vanilla JavaScript should give you enough understanding to implement this in the framework of your choice if there isn’t already a library that does it for you. Now we have a way to know when a navigation is being requested. Using the above utility function we can start the animation and replace our content as follows: ` getMyPageContentSomehow can be any function that returns HTML. How that is implemented will depend on your application and framework of choice. If you want to run these examples on your machine, the demo repository has instructions in its README. In essence, it’s as simple as hosting an HTTP server at the root of the project and visiting localhost. No fancy build system is required! By default, a fade is done that only lasts for a moment. The animation that happens can be configured using CSS with the ::view-transition-group pseudo-element on the element you want to animate, which in our case is the entire page, and we pass in root. ` Given that the animation properties are used, you have much control over what kind of animation to do. You can change the duration and the interpolation, add keyframes and gradients, and even add image masks. You can learn more about the animation properties in CSS on MDN. Using the View Transitions API for MPAs As mentioned, view transitions also work for MPAs with no client-side routing. Setting up view transitions for MPAs is much easier than for SPAs. All you have to do is include the CSS rule on all pages where you want the animations. ` Of course, like how it works with SPAs, you can customize the animations to your heart’s content using the view transition pseudo-elements. Conclusion I hope this article helped you understand the fundamentals of using the View Transitions API. Now that most browsers support it and it’s not too difficult to add it to existing applications, it is a great time to learn how to use it. You can view a full list of examples here (made by Jake Archibald and Bramus) if you want to see how advanced the animations can get. I like the Star Wars ones especially. The README explains how to get all the examples up and running (a total of 43!)....

Aug 2, 2024

4 mins

JavaScript

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

Mapping Returned HTTP Data with RxJS

In frontend development, it's likely that you will make API requests to retrieve data from some backend resource. However, some backends are set up in such a way that they either send too much data or not enough data back. When we combine what we know already about Reactive Programming and RxJS, we can handle these situations in a very elegant manner using some useful operators that RxJS provides us. In this article, we will look at handling both scenarios and look at four operators in particular: map, mergeMap, concatMap and switchMap. We will also provide links to some StackBlitz examples so you can see these live. For fun, we'll use the Star Wars API to fetch data and use Angular as our Frontend framework of choice as its HTTP library has Reactive Bindings out of the box. Handling too much data (part 1) Ok, let's set up the scenario. We want to find out some details about Luke Skywalker such as his name, birth year, height, weight, and eye color. With Angular, we can do this by simply making an HTTP request: ` If we do this, we _do_ get back the info we need, but we _also_ get back a lot of info we _don't_ need such as when the API entry was created and edited, Luke's species, his Vehicles etc. Right now, we don't care about those details. Let's see how we could use RxJS's map operator to only return the data we want. ` We can see from the example above that it's super easy to only pull the values you need from the response object! Note You can also see how we managed to map some of the fields in the response from snake_case to camelCase which is more of a convention in JavaScript _as well as_ mapping some fields in the response to a new name (mass -> weight). We can also convert some types to other types, such as mass as string to weight as number. This can be super helpful to keep the domain language of your frontend codebase intact. Live Example You can check this code out in action over at the live example here on StackBlitz. Feel free to fork it and play with it. Handling too much data (part 2) Another common use case of having too much data is search results. Some times we only want to display the first result from a bunch of search results. Let's set up a new scenario. We'll create a typeahead search that only shows the most relevant search result. We want to request search results after every key press the user makes; however, we also don't want to make requests that are not needed. Therefore, we want to cancel any inflight requests created as the user types. For this scenario, we'll be using a mix of the map and switchMap operators. We'll also use Angular's Reactive Forms Module to provide us with some reactive bindings. Our code for this is very simple: ` It's that simple to create an eager typeahead search with Angular and RxJS. You can see the live example of this here on StackBlitz. Handling too little data We've looked at how to handle too much data in the API response with RxJS, but how about when we have too little data? We can build this scenario out perfectly with the Star Wars API. Let's say we want to see what films the characters we are searching for appear in. The API response for the characters _does_ contain what films they are in, but it _does not_ give us details, just a URL that we can send a new request to get that film's data. This is also an Array of films so we _may_ want to get the details for all the films they appear in at this time. Let's see how we can transform our search code to allow us to fetch more data _related_ to the results and map it into the final object that we use to render the data. ` I highly recommend reading the code above and the comments to understand exactly how to achieve this scenario. This pattern is very powerful, especially for example if you need to iterate over an array of user IDs and fetch the user details associated with those IDs. There is also a live example of this here on StackBlitz that you can use to try it out. Conclusion This is a small introduction to mapping data returned from HTTP requests with RxJS, but hopefully you can see use this as a reference point if you ever need to perform complex data mapping that involves additional API requests....

Jan 4, 2021

4 mins

RxJSAngularJavaScript

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

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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

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