Upgrading from AngularJS

Angular is the name for the Angular of today and tomorrow. AngularJS is the name for all v1.x versions of Angular.

AngularJS apps are great. Always consider the business case before moving to Angular. An important part of that case is the time and effort to get there. This guide describes the built-in tools for efficiently migrating AngularJS projects over to the Angular platform, a piece at a time.

Some applications will be easier to upgrade than others, and there are ways in which we can make it easier for ourselves. It is possible to prepare and align AngularJS applications with Angular even before beginning the upgrade process. These preparation steps are all about making the code more decoupled, more maintainable, and up to speed with modern development tools. That means the preparation work will not only make the eventual upgrade easier, but will also generally improve our AngularJS applications.

One of the keys to a successful upgrade is to do it incrementally, by running the two frameworks side by side in the same application, and porting AngularJS components to Angular one by one. This makes it possible to upgrade even large and complex applications without disrupting other business, because the work can be done collaboratively and spread over a period of time. The upgrade module in Angular has been designed to make incremental upgrading seamless.

1. Preparation
   1. Follow the Angular Style Guide
   2. Using a Module Loader
   3. Migrating to TypeScript
   4. Using Component Directives
2. Upgrading with The Upgrade Module
   1. How The Upgrade Module Works
   2. Bootstrapping hybrid
   3. Using Angular Components from AngularJS Code
   4. Using AngularJS Component Directives from Angular Code
   5. Projecting AngularJS Content into Angular Components
   6. Transcluding Angular Content into AngularJS Component Directives
   7. Making AngularJS Dependencies Injectable to Angular
   8. Making Angular Dependencies Injectable to AngularJS
   9. Using Ahead-of-time compilation with hybrid apps
   10. Dividing routes between Angular and AngularJS
3. PhoneCat Upgrade Tutorial
   1. Switching to TypeScript
   2. Installing Angular
   3. Bootstrapping a hybrid PhoneCat
   4. Upgrading the Phone service
   5. Upgrading Components
   6. AoT compile the hybrid app
   7. Adding The Angular Router And Bootstrap
   8. Say Goodbye to AngularJS
4. Appendix: Upgrading PhoneCat Tests

Preparation

There are many ways to structure AngularJS applications. When we begin to upgrade these applications to Angular, some will turn out to be much more easy to work with than others. There are a few key techniques and patterns that we can apply to future proof our apps even before we begin the migration.

Follow the Angular Style Guide

The AngularJS Style Guide collects patterns and practices that have been proven to result in cleaner and more maintainable AngularJS applications. It contains a wealth of information about how to write and organize Angular code - and equally importantly - how not to write and organize Angular code.

Angular is a reimagined version of the best parts of AngularJS. In that sense, its goals are the same as the Angular Style Guide's: To preserve the good parts of AngularJS, and to avoid the bad parts. There's a lot more to Angular than just that of course, but this does mean that following the style guide helps make your AngularJS app more closely aligned with Angular.

There are a few rules in particular that will make it much easier to do an incremental upgrade using the Angular upgrade module:

• The Rule of 1 states that there should be one component per file. This not only makes components easy to navigate and find, but will also allow us to migrate them between languages and frameworks one at a time. In this example application, each controller, component, service, and filter is in its own source file.

• The Folders-by-Feature Structure and Modularity rules define similar principles on a higher level of abstraction: Different parts of the application should reside in different directories and Angular modules.

When an application is laid out feature per feature in this way, it can also be migrated one feature at a time. For applications that don't already look like this, applying the rules in the Angular style guide is a highly recommended preparation step. And this is not just for the sake of the upgrade - it is just solid advice in general!

Using a Module Loader

When we break application code down into one component per file, we often end up with a project structure with a large number of relatively small files. This is a much neater way to organize things than a small number of large files, but it doesn't work that well if you have to load all those files to the HTML page with <script> tags. Especially when you also have to maintain those tags in the correct order. That's why it's a good idea to start using a module loader.

Using a module loader such as SystemJS, Webpack, or Browserify allows us to use the built-in module systems of the TypeScript or ES2015 languages in our apps. We can use the import and export features that explicitly specify what code can and will be shared between different parts of the application. For ES5 applications we can use CommonJS style require and module.exports features. In both cases, the module loader will then take care of loading all the code the application needs in the correct order.

When we then take our applications into production, module loaders also make it easier to package them all up into production bundles with batteries included.

Migrating to TypeScript

If part of our Angular upgrade plan is to also take TypeScript into use, it makes sense to bring in the TypeScript compiler even before the upgrade itself begins. This means there's one less thing to learn and think about during the actual upgrade. It also means we can start using TypeScript features in our AngularJS code.

Since TypeScript is a superset of ECMAScript 2015, which in turn is a superset of ECMAScript 5, "switching" to TypeScript doesn't necessarily require anything more than installing the TypeScript compiler and switching renaming files from *.js to *.ts. But just doing that is not hugely useful or exciting, of course. Additional steps like the following can give us much more bang for the buck:

• For applications that use a module loader, TypeScript imports and exports (which are really ECMAScript 2015 imports and exports) can be used to organize code into modules.
• Type annotations can be gradually added to existing functions and variables to pin down their types and get benefits like build-time error checking, great autocompletion support and inline documentation.
• JavaScript features new to ES2015, like arrow functions, lets and consts, default function parameters, and destructuring assignments can also be gradually added to make the code more expressive.
• Services and controllers can be turned into classes. That way they'll be a step closer to becoming Angular service and component classes, which will make our life easier once we do the upgrade.

Using Component Directives

In Angular, components are the main primitive from which user interfaces are built. We define the different parts of our UIs as components, and then compose the UI by using components in our templates.

You can also do this in AngularJS, using component directives. These are directives that define their own templates, controllers, and input/output bindings - the same things that Angular components define. Applications built with component directives are much easier to migrate to Angular than applications built with lower-level features like ng-controller, ng-include, and scope inheritance.

To be Angular compatible, an AngularJS component directive should configure these attributes:

• restrict: 'E'. Components are usually used as elements.
• scope: {} - an isolate scope. In Angular, components are always isolated from their surroundings, and we should do this in AngularJS too.
• bindToController: {}. Component inputs and outputs should be bound to the controller instead of using the $scope.
• controller and controllerAs. Components have their own controllers.
• template or templateUrl. Components have their own templates.

Component directives may also use the following attributes:

• transclude: true, if the component needs to transclude content from elsewhere.
• require, if the component needs to communicate with some parent component's controller.

Component directives may not use the following attributes:

• compile. This will not be supported in Angular.
• replace: true. Angular never replaces a component element with the component template. This attribute is also deprecated in AngularJS.
• priority and terminal. While AngularJS components may use these, they are not used in Angular and it is better not to write code that relies on them.

An AngularJS component directive that is fully aligned with the Angular architecture may look something like this:

AngularJS 1.5 introduces the component API that makes it easier to define directives like these. It is a good idea to use this API for component directives for several reasons:

• It requires less boilerplate code.
• It enforces the use of component best practices like controllerAs.
• It has good default values for directive attributes like scope and restrict.

The component directive example from above looks like this when expressed using the component API:

Controller lifecycle hook methods $onInit(), $onDestroy(), and $onChanges() are another convenient feature that AngularJS 1.5 introduces. They all have nearly exact equivalents in Angular, so organizing component lifecycle logic around them will ease the eventual Angular upgrade process.

Upgrading with The Upgrade Module

The upgrade module in Angular is a very useful tool for upgrading anything but the smallest of applications. With it we can mix and match AngularJS and Angular components in the same application and have them interoperate seamlessly. That means we don't have to do the upgrade work all at once, since there's a natural coexistence between the two frameworks during the transition period.

How The Upgrade Module Works

The primary tool provided by the upgrade module is called the UpgradeModule. This is a service that can bootstrap and manage hybrid applications that support both Angular and AngularJS code.

When we use UpgradeModule, what we're really doing is running both versions of Angular at the same time. All Angular code is running in the Angular framework, and AngularJS code in the AngularJS framework. Both of these are the actual, fully featured versions of the frameworks. There is no emulation going on, so we can expect to have all the features and natural behavior of both frameworks.

What happens on top of this is that components and services managed by one framework can interoperate with those from the other framework. This happens in three main areas: Dependency injection, the DOM, and change detection.

Dependency Injection

Dependency injection is front and center in both AngularJS and Angular, but there are some key differences between the two frameworks in how it actually works.

Even accounting for these differences we can still have dependency injection interoperability. The UpgradeModule resolves the differences and makes everything work seamlessly:

• We can make AngularJS services available for injection to Angular code by upgrading them. The same singleton instance of each service is shared between the frameworks. In Angular these services will always be in the root injector and available to all components.
• We can also make Angular services available for injection to AngularJS code by downgrading them. Only services from the Angular root injector can be downgraded. Again, the same singleton instances are shared between the frameworks. When we register a downgrade, we explicitly specify a string token that we want to use in AngularJS.

Components and the DOM

What we'll find in the DOM of a hybrid application are components and directives from both AngularJS and Angular. These components communicate with each other by using the input and output bindings of their respective frameworks, which the UpgradeModule bridges together. They may also communicate through shared injected dependencies, as described above.

There are two key things to understand about what happens in the DOM of a hybrid application:

1. Every element in the DOM is owned by exactly one of the two frameworks. The other framework ignores it. If an element is owned by AngularJS, Angular treats it as if it didn't exist, and vice versa.
2. The root of the application is always an AngularJS template.

So a hybrid application begins life as an AngularJS application, and it is AngularJS that processes its root template. Angular then steps into the picture when an Angular component is used somewhere in the application templates. That component's view will then be managed by Angular, and it may use any number of Angular components and directives.

Beyond that, we may interleave the two frameworks as much as we need to. We always cross the boundary between the two frameworks by one of two ways:

1. By using a component from the other framework: An AngularJS template using an Angular component, or an Angular template using an AngularJS component.
2. By transcluding or projecting content from the other framework. The UpgradeModule bridges the related concepts of AngularJS transclusion and Angular content projection together.

Whenever we use a component that belongs to the other framework, a switch between framework boundaries occurs. However, that switch only happens to the children of the component element. Consider a situation where we use an Angular component from AngularJS like this:

The DOM element <a-component> will remain to be an AngularJS managed element, because it's defined in an AngularJS template. That also means you can apply additional AngularJS directives to it, but not Angular directives. It is only in the template of the <a-component> where Angular steps in. This same rule also applies when you use AngularJS component directives from Angular.

Change Detection

Change detection in AngularJS is all about scope.$apply(). After every event that occurs, scope.$apply() gets called. This is done either automatically by the framework, or in some cases manually by our own code. It is the point in time when change detection occurs and data bindings get updated.

In Angular things are different. While change detection still occurs after every event, no one needs to call scope.$apply() for that to happen. This is because all Angular code runs inside something called the Angular zone. Angular always knows when the code finishes, so it also knows when it should kick off change detection. The code itself doesn't have to call scope.$apply() or anything like it.

In the case of hybrid applications, the UpgradeModule bridges the AngularJS and Angular approaches. Here's what happens:

• Everything that happens in the application runs inside the Angular zone. This is true whether the event originated in AngularJS or Angular code. The zone triggers Angular change detection after every event.
• The UpgradeModule will invoke the AngularJS $rootScope.$apply() after every turn of the Angular zone. This also triggers AngularJS change detection after every event.

What this means in practice is that we do not need to call $apply() in our code, regardless of whether it is in AngularJS on Angular. The UpgradeModule does it for us. We can still call $apply() so there is no need to remove such calls from existing code. Those calls just don't have any effect in a hybrid application.

When we downgrade an Angular component and then use it from AngularJS, the component's inputs will be watched using AngularJS change detection. When those inputs change, the corresponding properties in the component are set. We can also hook into the changes by implementing the OnChanges interface in the component, just like we could if it hadn't been downgraded.

Correspondingly, when we upgrade an AngularJS component and use it from Angular, all the bindings defined for the component directive's scope (or bindToController) will be hooked into Angular change detection. They will be treated as regular Angular inputs and set onto the scope (or controller) when they change.

Using UpgradeModule with Angular NgModules

Both AngularJS and Angular have their own concept of modules to help organize an application into cohesive blocks of functionality.

Their details are quite different in architecture and implementation. In AngularJS, you add Angular assets to the angular.module property. In Angular, you create one or more classes adorned with an NgModule decorator that describes Angular assets in metadata. The differences blossom from there.

In a hybrid application we run both versions of Angular at the same time. That means that we need at least one module each from both AngularJS and Angular. We will import UpgradeModule inside our Angular module, and then use it for bootstrapping our AngularJS module. Let's see how.

Bootstrapping hybrid applications

The first step to upgrading an application using the UpgradeModule is always to bootstrap it as a hybrid that supports both AngularJS and Angular, but still is an AngularJS app at top level.

Pure AngularJS applications can be bootstrapped in two ways: By using an ng-app directive somewhere on the HTML page, or by calling angular.bootstrap from JavaScript. In Angular, only the second method is possible - there is no ng-app in Angular. This is also the case for hybrid applications. Therefore, it is a good preliminary step to switch AngularJS applications to use the JavaScript bootstrap method even before switching them to hybrid mode.

Say we have an ng-app driven bootstrap such as this one:

We can remove the ng-app and ng-strict-di directives from the HTML and instead switch to calling angular.bootstrap from JavaScript, which will result in the same thing:

Now introduce Angular to the project. Inspired by instructions in the Setup, you can selectively copy in material from the QuickStart github repository.

Next, create an app.module.ts file and add the following NgModule class:

This bare minimum NgModule imports BrowserModule, the module every Angular browser-based app must have.

It also imports UpgradeModule from @angular/upgrade/static, and adds an override to prevent Angular from bootstrapping itself in the form of the ngDoBootstrap empty class method.

Now we bootstrap AppModule using platformBrowserDynamic's bootstrapModule method. Then we use dependency injection to get a hold of the UpgradeModule instance in AppModule, and use it to bootstrap our AngularJS app. The upgrade.bootstrap method takes the exact same arguments as angular.bootstrap:

We also need to install the @angular/upgrade package via npm install @angular/upgrade --save and add a mapping for the @angular/upgrade/static package:

Congratulations! You're running a hybrid application! The existing AngularJS code works as before and you're ready to run Angular code.

Using Angular Components from AngularJS Code

Once we're running a hybrid app, we can start the gradual process of upgrading code. One of the more common patterns for doing that is to use an Angular component in an AngularJS context. This could be a completely new component or one that was previously AngularJS but has been rewritten for Angular.

Say we have a simple Angular component that shows information about a hero:

If we want to use this component from AngularJS, we need to downgrade it using the downgradeComponent() method. What we get when we do that is an AngularJS directive, which we can then register into our AngularJS module:

Because HeroDetailComponent is an Angular component, we must also add it to the declarations in the AppModule.

And because this component is being used from the AngularJS module, and is an entry point into our Angular application, we also need to add it to the entryComponents for our Angular module.

The net result is an AngularJS directive called heroDetail, that we can use like any other directive in our AngularJS templates.

Most components are not quite this simple, of course. Many of them have inputs and outputs that connect them to the outside world. An Angular hero detail component with inputs and outputs might look like this:

These inputs and outputs can be supplied from the AngularJS template, and the downgradeComponent() method takes care of bridging them over via the inputs and outputs arrays:

Note that even though we are in an AngularJS template, we're using Angular attribute syntax to bind the inputs and outputs. This is a requirement for downgraded components. The expressions themselves are still regular AngularJS expressions.

The $event variable can be used in outputs to gain access to the object that was emitted. In this case it will be the Hero object, because that is what was passed to this.deleted.emit().

Since this is an AngularJS template, we can still use other AngularJS directives on the element, even though it has Angular binding attributes on it. For example, we can easily make multiple copies of the component using ng-repeat:

Using AngularJS Component Directives from Angular Code

So, we can write an Angular component and then use it from AngularJS code. This is very useful when we start our migration from lower-level components and work our way up. But in some cases it is more convenient to do things in the opposite order: To start with higher-level components and work our way down. This too can be done using the UpgradeModule. We can upgrade AngularJS component directives and then use them from Angular.

Not all kinds of AngularJS directives can be upgraded. The directive really has to be a component directive, with the characteristics described in the preparation guide above. Our safest bet for ensuring compatibility is using the component API introduced in AngularJS 1.5.

A simple example of an upgradable component is one that just has a template and a controller:

We can upgrade this component to Angular using the UpgradeComponent class. By creating a new Angular directive that extends UpgradeComponent and doing a super call inside it's constructor, we have a fully upgrade AngularJS component to be used inside Angular. All that is left is to add it to AppModule's declarations array.

An upgraded component may also have inputs and outputs, as defined by the scope/controller bindings of the original AngularJS component directive. When we use the component from an Angular template, we provide the inputs and outputs using Angular template syntax, with the following rules:

As an example, say we have a hero detail AngularJS component directive with one input and one output:

We can upgrade this component to Angular, annotate inputs and outputs in the upgrade directive, and then provide the input and output using Angular template syntax:

Projecting AngularJS Content into Angular Components

When we are using a downgraded Angular component from an AngularJS template, the need may arise to transclude some content into it. This is also possible. While there is no such thing as transclusion in Angular, there is a very similar concept called content projection. The UpgradeModule is able to make these two features interoperate.

Angular components that support content projection make use of an <ng-content> tag within them. Here's an example of such a component:

When using the component from AngularJS, we can supply contents for it. Just like they would be transcluded in AngularJS, they get projected to the location of the <ng-content> tag in Angular:

Transcluding Angular Content into AngularJS Component Directives

Just like we can project AngularJS content into Angular components, we can transclude Angular content into AngularJS components, whenever we are using upgraded versions from them.

When an AngularJS component directive supports transclusion, it may use the ng-transclude directive in its template to mark the transclusion point:

If we upgrade this component and use it from Angular, we can populate the component tag with contents that will then get transcluded:

Making AngularJS Dependencies Injectable to Angular

When running a hybrid app, we may bump into situations where we need to have some AngularJS dependencies to be injected to Angular code. This may be because we have some business logic still in AngularJS services, or because we need some of AngularJS's built-in services like $location or $timeout.

In these situations, it is possible to upgrade an AngularJS provider to Angular. This makes it possible to then inject it somewhere in Angular code. For example, we might have a service called HeroesService in AngularJS:

We can upgrade the service using a Angular Factory provider that requests the service from the AngularJS $injector.

We recommend declaring the Factory Provider in a separate ajs-upgraded-providers.ts file so that they are all together, making it easier to reference them, create new ones and delete them once the upgrade is over.

It's also recommended to export the heroesServiceFactory function so that Ahead-of-Time compilation can pick it up.

We can then inject it in Angular using it's class as a type annotation:

Making Angular Dependencies Injectable to AngularJS

In addition to upgrading AngularJS dependencies, we can also downgrade Angular dependencies, so that we can use them from AngularJS. This can be useful when we start migrating services to Angular or creating new services in Angular while we still have components written in AngularJS.

For example, we might have an Angular service called Heroes:

Again, as with Angular components, register the provider with the NgModule by adding it to the module's providers list.

Now wrap the Angular Heroes in an AngularJS factory function using downgradeInjectable(). and plug the factory into an AngularJS module. The name of the AngularJS dependency is up to you:

After this, the service is injectable anywhere in our AngularJS code:

Using Ahead-of-time compilation with hybrid apps

We can take advantage of Ahead-of-time (AoT) compilation on hybrid apps just like on any other Angular application. The setup for an hybrid app is mostly the same as described in the Ahead-of-time Compilation chapter save for differences in index.html and main-aot.ts

Our index.html will likely have script tags loading AngularJS files, so the index.html we use for AoT must also load those files. An easy way to copy them is by adding each to the copy-dist-files.js file.

We also need to use UpgradeModule to bootstrap a hybrid app after bootstrapping the Module Factory:

And that's all we need to get the full benefit of AoT for Angular apps!

Dividing routes between Angular and AngularJS

Another important part of upgrading is upgrading routes. We could upgrade our whole app while still using the AngularJS router and then migrate all the routes in one fell swoop. But it would be much better to migrate routes one by one as they become upgraded.

The first step to have a dual router setup is to add an Angular root component containing one outlet for each router. AngularJS will use ng-view, and Angular will use router-outlet. When one is using it's router, the other outlet will be empty.

We want to use this component in the body of our index.html instead of an AngularJS component:

Next we declare both AngularJS and Angular routes as normal:

In our app.module.ts we need to add AppComponent to the declarations and boostrap array.

Next we configure the router itself. We want to use hash navigation in Angular because that's what we're also using in AngularJS.

Lastly, and most importantly, we want to use a custom UrlHandlingStrategy that will tell the Angular router which routes it should render - and only those.

That's it! Now we're running both routers at the same time.

PhoneCat Upgrade Tutorial

In this section and we will look at a complete example of preparing and upgrading an application using the upgrade module. The app we're going to work on is Angular PhoneCat from the original AngularJS tutorial, which is where many of us began our Angular adventures. Now we'll see how to bring that application to the brave new world of Angular.

During the process we'll learn how to apply the steps outlined in the preparation guide in practice: We'll align the application with Angular and also take TypeScript into use.

To follow along with the tutorial, clone the angular-phonecat repository and apply the steps as we go.

In terms of project structure, this is where our work begins:

This is actually a pretty good starting point. The code uses the AngularJS 1.5 component API and the organization follows the AngularJS Style Guide, which is an important preparation step before a successful upgrade.

• Each component, service, and filter is in its own source file, as per the Rule of 1.
• The core, phone-detail, and phone-list modules are each in their own subdirectory. Those subdirectories contain the JavaScript code as well as the HTML templates that go with each particular feature. This is in line with the Folders-by-Feature Structure and Modularity rules.
• Unit tests are located side-by-side with application code where they are easily found, as described in the rules for Organizing Tests.

Switching to TypeScript

Since we're going to be writing our Angular code in TypeScript, it makes sense to bring in the TypeScript compiler even before we begin upgrading.

We will also start to gradually phase out the Bower package manager in favor of NPM. We'll install all new dependencies using NPM, and will eventually be able to remove Bower from the project.

Let's begin by installing TypeScript to the project.

Let's also add run scripts for the tsc TypeScript compiler to package.json:

We can now install type definitions for the existing libraries that we're using but that don't come with prepackaged types: AngularJS and the Jasmine unit test framework.

We should also configure the TypeScript compiler so that it can understand our project. We'll add a tsconfig.json file to the project directory, just like we do in the documentation setup. It instructs the TypeScript compiler how to interpret our source files.

We are telling the TypeScript compiler to turn our TypeScript files to ES5 code bundled into CommonJS modules.

We can now launch the TypeScript compiler from the command line. It will watch our .ts source files and compile them to JavaScript on the fly. Those compiled .js files are then loaded into the browser by SystemJS. This is a process we'll want to have continuously running in the background as we go along.

The next thing we'll do is convert our JavaScript files to TypeScript. Since TypeScript is a superset of ECMAScript 2015, which in turn is a superset of ECMAScript 5, we can simply switch the file extensions from .js to .ts and everything will work just like it did before. As the TypeScript compiler runs, it emits the corresponding .js file for every .ts file and the compiled JavaScript is what actually gets executed. If you start the project HTTP server with npm start, you should see the fully functional application in your browser.

Now that we have TypeScript though, we can start benefiting from some of its features. There's a lot of value the language can provide to AngularJS applications.

For one thing, TypeScript is a superset of ES2015. Any app that has previously been written in ES5 - like the PhoneCat example has - can with TypeScript start incorporating all of the JavaScript features that are new to ES2015. These include things like lets and consts, arrow functions, default function parameters, and destructuring assignments.

Another thing we can do is start adding type safety to our code. This has actually partially already happened because of the AngularJS typings we installed. TypeScript are checking that we are calling AngularJS APIs correctly when we do things like register components to Angular modules.

But we can also start adding type annotations for our own code to get even more out of TypeScript's type system. For instance, we can annotate the checkmark filter so that it explicitly expects booleans as arguments. This makes it clearer what the filter is supposed to do.

In the Phone service we can explicitly annotate the $resource service dependency as an angular.resource.IResourceService - a type defined by the AngularJS typings.

We can apply the same trick to the application's route configuration file in app.config.ts, where we are using the location and route services. By annotating them accordingly TypeScript can verify we're calling their APIs with the correct kinds of arguments.

Another TypeScript feature we can make use of is classes. In particular, we can turn our component controllers into classes. That way they'll be a step closer to becoming Angular component classes, which will make our life easier once we do the upgrade.

AngularJS expects controllers to be constructor functions. That's exactly what ES2015/TypeScript classes are under the hood, so that means we can just plug in a class as a component controller and AngularJS will happily use it.

Here's what our new class for the phone list component controller looks like:

What was previously done in the controller function is now done in the class constructor function. The dependency injection annotations are attached to the class using a static property $inject. At runtime this becomes the PhoneListController.$inject property.

The class additionally declares three members: The array of phones, the name of the current sort key, and the search query. These are all things we have already been attaching to the controller but that weren't explicitly declared anywhere. The last one of these isn't actually used in the TypeScript code since it's only referred to in the template, but for the sake of clarity we want to define all the members our controller will have.

In the Phone detail controller we'll have two members: One for the phone that the user is looking at and another for the URL of the currently displayed image:

This makes our controller code look a lot more like Angular already. We're all set to actually introduce Angular into the project.

If we had any AngularJS services in the project, those would also be a good candidate for converting to classes, since like controllers, they're also constructor functions. But we only have the Phone factory in this project, and that's a bit special since it's an ngResource factory. So we won't be doing anything to it in the preparation stage. We'll instead turn it directly into an Angular service.

Installing Angular

Having completed our preparation work, let's get going with the Angular upgrade of PhoneCat. We'll do this incrementally with the help of the upgrade module that comes with Angular. By the time we're done, we'll be able to remove AngularJS from the project completely, but the key is to do this piece by piece without breaking the application.

Let's install Angular into the project, along with the SystemJS module loader. Take a look at the results of the Setup instructions and get the following configurations from there:

• Add Angular and the other new dependencies to package.json
• The SystemJS configuration file systemjs.config.js to the project root directory.

Once these are done, run:

We can soon load Angular dependencies into the application via index.html, but first we need to do some directory path adjustments. This is because we're going to need to load files from node_modules and the project root, whereas so far in this project everything has been loaded from the /app directory.

Move the app/index.html file to the project root directory. Then change the development server root path in package.json to also point to the project root instead of app:

Now we're able to serve everything from the project root to the web browser. But we do not want to have to change all the image and data paths used in the application code to match our development setup. For that reason, we'll add a <base> tag to index.html, which will cause relative URLs to be resolved back to the /app directory:

Now we can load Angular via SystemJS. We'll add the Angular polyfills and the SystemJS config to the end of the <head> section, and then we'll use System.import to load the actual application:

We also need to make a couple of adjustments to the systemjs.config.js file installed during setup.

We want to point the browser to the project root when loading things through SystemJS, instead of using the <base> URL.

We also need to install the upgrade package via npm install @angular/upgrade --save and add a mapping for the @angular/upgrade/static package.

Creating the AppModule

Now create the root NgModule class called AppModule. There is already a file named app.module.ts that holds the AngularJS module. Rename it to app.module.ajs.ts and update the corresponding script name in the index.html as well. The file contents remain:

Now create a new app.module.ts with the minimum NgModule class:

Bootstrapping a hybrid PhoneCat

What we'll do next is bootstrap the application as a hybrid application that supports both AngularJS and Angular components. Once we've done that we can start converting the individual pieces to Angular.

To bootstrap a hybrid application, we first need to import UpgradeModule in our AppModule, and override it's bootstrap method:

Our application is currently bootstrapped using the AngularJS ng-app directive attached to the <html> element of the host page. This will no longer work with Angular. We should switch to a JavaScript-driven bootstrap instead.

So, remove the ng-app attribute from index.html, and instead bootstrap via src/main.ts. This file has been configured as the application entrypoint in systemjs.config.js, so it is already being loaded by the browser.

The arguments used here are the root element of the application (which is the same element we had ng-app on earlier), and the AngularJS 1.x modules that we want to load. Since we're bootstrapping the app through an UpgradeModule, we're actually now running the app as a hybrid app.

This means we are now running both AngularJS and Angular at the same time. That's pretty exciting! We're not running any actual Angular components yet though, so let's do that next.

Upgrading the Phone service

The first piece we'll port over to Angular is the Phone service, which resides in app/core/phone/phone.service.ts and makes it possible for components to load phone information from the server. Right now it's implemented with ngResource and we're using it for two things:

• For loading the list of all phones into the phone list component
• For loading the details of a single phone into the phone detail component.

We can replace this implementation with an Angular service class, while keeping our controllers in AngularJS land.

In the new version, we import the Angular HTTP module and call its Http service instead of ngResource.

Re-open the app.module.ts file, import and add HttpModule to the imports array of the AppModule:

Now we're ready to upgrade the Phone service itself. We replace the ngResource-based service in phone.service.ts with a TypeScript class decorated as @Injectable:

The @Injectable decorator will attach some dependency injection metadata to the class, letting Angular know about its dependencies. As described by our Dependency Injection Guide, this is a marker decorator we need to use for classes that have no other Angular decorators but still need to have their dependencies injected.

In its constructor the class expects to get the Http service. It will be injected to it and it is stored as a private field. The service is then used in the two instance methods, one of which loads the list of all phones, and the other the details of a particular phone:

The methods now return Observables of type PhoneData and PhoneData[]. This is a type we don't have yet, so let's add a simple interface for it:

@angular/upgrade/static has a downgradeInjectable method for the purpose of making Angular services available to AngularJS code. Use it to plug in the Phone service:

Here's the full, final code for the service:

Notice that we're importing the map operator of the RxJS Observable separately. We need to do this for all RxJS operators that we want to use, since Angular does not load all of them by default.

The new Phone service has the same features as the original, ngResource-based service. Because it's an Angular service, we register it with the NgModule providers:

Now that we are loading phone.service.ts through an import that is resolved by SystemJS, we should remove the <script> tag for the service from index.html. This is something we'll do to all our components as we upgrade them. Simultaneously with the AngularJS to Angular upgrade we're also migrating our code from scripts to modules.

At this point we can switch our two components to use the new service instead of the old one. We $inject it as the downgraded phone factory, but it's really an instance of the Phone class and we can annotate its type accordingly:

What we have here are two AngularJS components using an Angular service! The components don't need to be aware of this, though the fact that the service returns Observables and not Promises is a bit of a giveaway. In any case, what we've achieved is a migration of a service to Angular without having to yet migrate the components that use it.

Upgrading Components

Next, let's upgrade our AngularJS components to Angular components. We'll do it one at a time, while still keeping the application in hybrid mode. As we make these conversions, we'll also be defining our first Angular pipes.

Let's look at the phone list component first. Right now it contains a TypeScript controller class and a component definition object. We can morph this into an Angular component by just renaming the controller class and turning the AngularJS component definition object into an Angular @Component decorator. We can then also remove the static $inject property from the class:

The selector attribute is a CSS selector that defines where on the page the component should go. In AngularJS we do matching based on component names, but in Angular we have these explicit selectors. This one will match elements with the name phone-list, just like the AngularJS version did.

We now also need to convert the template of this component into Angular syntax. The search controls replace the AngularJS $ctrl expressions with Angular's two-way [(ngModel)] binding syntax:

Replace the list's ng-repeat with an *ngFor as described in the Template Syntax page. Replace the image tag's ng-src with a binding to the native src property.

No Angular filter or orderBy filters

The built-in AngularJS filter and orderBy filters do not exist in Angular, so we need to do the filtering and sorting ourselves.

We replaced the filter and orderBy filters with bindings to the getPhones() controller method, which implements the filtering and ordering logic inside the component itself.

Now we need to downgrade our Angular component so we can use it in AngularJS. Instead of registering a component, we register a phoneList directive, a downgraded version of the Angular component.

The as angular.IDirectiveFactory cast tells the TypeScript compiler that the return value of the downgradeComponent method is a directive factory.

The new PhoneListComponent uses the Angular ngModel directive, located in the FormsModule. Add the FormsModule to NgModule imports, declare the new PhoneListComponent and finally add it to entryComponents since we downgraded it:

Remove the <script> tag for the phone list component from index.html.

Now set the remaining phone-detail.component.ts as follows:

This is similar to the phone list component. The new wrinkle is the RouteParams type annotation that identifies the routeParams dependency.

The AngularJS injector has an AngularJS router dependency called $routeParams, which was injected into PhoneDetails when it was still an AngularJS controller. We intend to inject it into the new PhoneDetailsComponent.

Unfortunately, AngularJS dependencies are not automatically available to Angular components. We must use a Factory provider to make $routeParams an Angular provider. Do that in a new file called ajs-upgraded-providers.ts and import it in app.module.ts:

Convert the phone detail component template into Angular syntax as follows:

There are several notable changes here:

• We've removed the $ctrl. prefix from all expressions.
• Just like we did in the phone list, we've replaced ng-src with property bindings for the standard src property.
• We're using the property binding syntax around ng-class. Though Angular does have a very similar ngClass as AngularJS does, its value is not magically evaluated as an expression. In Angular we always specify in the template when an attribute's value is a property expression, as opposed to a literal string.
• We've replaced ng-repeats with *ngFors.
• We've replaced ng-click with an event binding for the standard click.
• We've wrapped the whole template in an ngIf that causes it only to be rendered when there is a phone present. We need this because when the component first loads, we don't have phone yet and the expressions will refer to a non-existing value. Unlike in AngularJS, Angular expressions do not fail silently when we try to refer to properties on undefined objects. We need to be explicit about cases where this is expected.

Add PhoneDetailComponent component to the NgModule declarations and entryComponents:

We should now also remove the phone detail component <script> tag from index.html.

Add the CheckmarkPipe

The AngularJS directive had a checkmark filter. Let's turn that into an Angular pipe.

There is no upgrade method to convert filters into pipes. You won't miss it. It's easy to turn the filter function into an equivalent Pipe class. The implementation is the same as before, repackaged in the transform method. Rename the file to checkmark.pipe.ts to conform with Angular conventions:

Now import and declare the newly created pipe and remove the filter <script> tag from index.html:

AoT compile the hybrid app

To use AoT with our hybrid app we have to first set it up like any other Angular application, as shown in the Ahead-of-time Compilation chapter.

Then we have to change main-aot.ts bootstrap also bootstrap the AngularJS app via UpgradeModule:

We need to load all the AngularJS files we already use in index.html in aot/index.html as well:

These files need to be copied together with the polyfills. Files our application needs at runtime, like the .json phone lists and images, also need to be copied.

Install fs-extra via npm install fs-extra --save-dev for better file copying, and change copy-dist-files.js to the following:

And that's all you need to use AoT while upgrading your app!

Adding The Angular Router And Bootstrap

At this point we've replaced all AngularJS application components with their Angular counterparts, even though we're still serving them from the AngularJS router.

Most AngularJS apps have more than a couple of routes though, and it's very helpful to migrate one route at a time.

Let's start by migrating the initial / and /phones routes to Angular, while keeping /phones/:phoneId in the AngularJS router.

Add the Angular router

Angular has an all-new router.

Like all routers, it needs a place in the UI to display routed views. For Angular that's the <router-outlet> and it belongs in a root component at the top of the applications component tree.

We don't yet have such a root component, because the app is still managed as an AngularJS app. Create a new app.component.ts file with the following AppComponent class:

It has a simple template that only includes the <router-outlet> for Angular routes and ng-view for AngularJS routes. This component just renders the contents of the active route and nothing else.

The selector tells Angular to plug this root component into the <phonecat-app> element on the host web page when the application launches.

Add this <phonecat-app> element to the index.html. It replaces the old AngularJS ng-view directive:

Create the Routing Module

A router needs configuration whether it's the AngularJS or Angular or any other router.

The details of Angular router configuration are best left to the Routing documentation which recommends that you create a NgModule dedicated to router configuration (called a Routing Module).

This module defines a routes object with one route to the phone list component and a default route for the empty path. It passes the routes to the RouterModule.forRoot method which does the rest.

A couple of extra providers enable routing with "hash" URLs such as #!/phones instead of the default "push state" strategy.

There's a twist to our Routing Module though: we're also adding a custom UrlHandlingStrategy that tells the Angular router to only process the / and /phones routes.

Now update the AppModule to import this AppRoutingModule and also the declare the root AppComponent as the bootstrap component. That tells Angular that it should bootstrap the app with the root AppComponent and insert it's view into the host web page.

We can also remove the ngDoBootstrap() override from app.module.ts since we are now bootstrapping from Angular.

And since PhoneListComponent isn't being rendered from a <phone-list> tag anymore, but rather routed to, we can do away with it's Angular selector as well.

Now we need to tell the AngularJS router to only process the /phones/:phoneId route:

Generate links for each phone

We no longer have to hardcode the links to phone details in the phone list. We can generate data bindings for each phone's id to the routerLink directive and let that directive construct the appropriate URL to the PhoneDetailComponent:

We are now running both routers at the same time! Angular is handling the initial / url, redirecting to /phones. Meanwhile when we click a link to the phone detail, AngularJS takes over.

This way we can incrementally upgrade our app, reducing the risk of a massive one step router swap.

The next step is to migrate the /phones/:phoneId route.

The Angular router passes route parameters differently. Correct the PhoneDetail component constructor to expect an injected ActivatedRoute object. Extract the phoneId from the ActivatedRoute.snapshot.params and fetch the phone data as before:

Since this was the last route we want to migrate over, we can also now delete the last route config from app/app.config.ts, and add it to the Angular router configuration.

We don't need our UrlHandlingStrategy anymore either, since now Angular is processing all routes.

You are now running a pure Angular application!

Say Goodbye to AngularJS

It is time to take off the training wheels and let our application begin its new life as a pure, shiny Angular app. The remaining tasks all have to do with removing code - which of course is every programmer's favorite task!

The application is still bootstrapped as a hybrid app. There's no need for that anymore.

Switch the bootstrap method of the application from the UpgradeAdapter to the Angular way.

If you haven't already, remove all references to the UpgradeModule from app.module.ts, as well as any Factory provider for AngularJS services, and the app/ajs-upgraded-providers.ts file.

Also remove any downgradeInjectable() or downgradeComponent() you find, together with the associated AngularJS factory or directive declarations. Since we have no downgraded components anymore, we also don't need to have them listed in entryComponents either.

You may also completely remove the following files. They are AngularJS module configuration files and not needed in Angular:

• app/app.module.ajs.ts
• app/app.config.ts
• app/core/core.module.ts
• app/core/phone/phone.module.ts
• app/phone-detail/phone-detail.module.ts
• app/phone-list/phone-list.module.ts

The external typings for AngularJS may be uninstalled as well. The only ones we still need are for Jasmine and Angular polyfills. The @angular/upgrade package and it's mapping in systemjs.config.js can also go.

Finally, from index.html, remove all references to AngularJS scripts, the Angular upgrade module, and jQuery. When we're done, this is what it should look like:

That is the last we'll see of AngularJS! It has served us well but now it's time to say goodbye.

Appendix: Upgrading PhoneCat Tests

Tests can not only be retained through an upgrade process, but they can also be used as a valuable safety measure when ensuring that the application does not break during the upgrade. E2E tests are especially useful for this purpose.

E2E Tests

The PhoneCat project has both E2E Protractor tests and some Karma unit tests in it. Of these two, E2E tests can be dealt with much more easily: By definition, E2E tests access our application from the outside by interacting with the various UI elements the app puts on the screen. E2E tests aren't really that concerned with the internal structure of the application components. That also means that although we modify our project quite a bit during the upgrade, the E2E test suite should keep passing with just minor modifications. This is because we don't change how the application behaves from the user's point of view.

During TypeScript conversion, there is nothing we have to do to keep E2E tests working. It is only when we change our bootstrap to that of a Hybrid app that we need to make some changes.

The following change is needed in protractor-conf.js to sync with hybrid apps:

The next set of changes is when we start to upgrade components and their template to Angular. This is because the E2E tests have matchers that are specific to AngularJS. For PhoneCat we need to make the following changes in order to make things work with Angular:

When the bootstrap method is switched from that of UpgradeModule to pure Angular, AngularJS ceases to exist on the page completely. At this point we need to tell Protractor that it should not be looking for an AngularJS app anymore, but instead it should find Angular apps from the page.

Replace the ng12Hybrid previously added with the following in protractor-conf.js:

Also, there are a couple of Protractor API calls in the PhoneCat test code that are using the AngularJS $location service under the hood. As that service is no longer there after the upgrade, we need to replace those calls with ones that use WebDriver's generic URL APIs instead. The first of these is the redirection spec:

And the second is the phone links spec:

Unit Tests

For unit tests, on the other hand, more conversion work is needed. Effectively they need to be upgraded along with the production code.

During TypeScript conversion no changes are strictly necessary. But it may be a good idea to convert the unit test code into TypeScript as well, as the same benefits we from TypeScript in production code also applies to tests.

For instance, in the phone detail component spec we can use not only ES2015 features like arrow functions and block-scoped variables, but also type definitions for some of the AngularJS services we're consuming:

Once we start the upgrade process and bring in SystemJS, configuration changes are needed for Karma. We need to let SystemJS load all the new Angular code, which can be done with the following kind of shim file:

The shim first loads the SystemJS configuration, then Angular's test support libraries, and then the application's spec files themselves.

Karma configuration should then be changed so that it uses the application root dir as the base directory, instead of app.

Once this is done, we can load SystemJS and other dependencies, and also switch the configuration for loading application files so that they are not included to the page by Karma. We'll let the shim and SystemJS load them.

Since the HTML templates of Angular components will be loaded as well, we need to help Karma out a bit so that it can route them to the right paths:

The unit test files themselves also need to be switched to Angular when their production counterparts are switched. The specs for the checkmark pipe are probably the most straightforward, as the pipe has no dependencies:

The unit test for the phone service is a bit more involved. We need to switch from the mocked-out AngularJS $httpBackend to a mocked-out Angular Http backend.

For the component specs we can mock out the Phone service itself, and have it provide canned phone data. We use Angular's component unit testing APIs for both components.

Finally, we need to revisit both of the component tests when we switch to the Angular router. For the details component we need to provide a mock of Angular ActivatedRoute object instead of using the AngularJS $routeParams.

And for the phone list component we need to set up a few things for the router itself so that the route link directive will work.