5 Min Quickstart

Let's start from zero and build a super simple Angular 2 application in JavaScript.

See It Run!

Running the live example is the quickest way to see an Angular 2 app come to life.

Clicking that link fires up a browser, loads the sample in plunker, and displays a simple message:

Here is the file structure:

Functionally, it's an index.html and two JavaScript files in an app/ folder. We can handle that!

Of course we won't build many apps that only run in plunker. Let's follow a process that's closer to what we'd do in real life.

1. Set up our development environment
2. Write the Angular root component for our app
3. Bootstrap it to take control of the main web page
4. Write the main page (index.html)

Development Environment

We'll need a place to stand (the application project folder), some libraries and your editor of choice.

Create a new project folder

Add the libraries we need

We recommend the npm package manager for acquiring and managing our development libraries.

Add a package.json file to the project folder and copy/paste the following:

Install these packages by opening a terminal window (command window in Windows) and running this npm command.

Our First Angular Component

The Component is the most fundamental of Angular concepts. A component manages a view - a piece of the web page where we display information to the user and respond to user feedback.

Technically, a component is a class that controls a view template. We'll write a lot of them as we build Angular apps. This is our first attempt so we'll keep it ridiculously simple.

Create an application source sub-folder

We like to keep our application code in a sub-folder off the root called app/. Execute the following command in the console window.

Add the component file

Now add a file named app.component.js and paste the following lines:

We're creating a visual component named AppComponent by chaining the Component and Class methods that belong to the global Angular core namespace, ng.core.

The Component method takes a configuration object with two properties. The Class method is where we implement the component itself, giving it properties and methods that bind to the view and whatever behavior is appropriate for this part of the UI.

Let's review this file in detail.

Modules

Angular apps are modular. They consist of many files each dedicated to a purpose. ES5 JavaScript doesn't have modules, but we don't want to pollute the global namespace.

So we'll surround the code in a simple IIFE ("Immediately Invoked Function Expression"). It receives our app 'namespace' object as argument. We call our IIFE with window.app if it exists - and if it doesn't we initialize it as an empty object.

Most application files export one thing into our faux-pas 'namespace', such as a component. Our app.component.js file exports the AppComponent.

A more sophisticated application would have child components that descended from AppComponent in a visual tree. A more sophisticated app would have more files and modules, at least as many as it had components.

Quickstart isn't sophisticated; one component is all we need. Yet modules play a fundamental organizational role in even this small app.

Modules rely on other modules. In JavaScript Angular apps, when we need something provided by another module, we get it from the app object. When another module needs to refer to AppComponent, it gets it from the app.AppComponent like this:

Angular is also modular. It is a collection of library modules. Each library is itself a module made up of several, related feature modules.

When we need something from Angular, we use the ng object.

The Class definition object

At the bottom of the file is an empty, do-nothing class definition object for our AppComponent class. When we're ready to build a substantive application, we can expand this object with properties and application logic. Our AppComponent class has nothing but an empty constructor because we don't need it to do anything in this QuickStart.

The Component definition object

ng.core.Component() tells Angular that this class definition object is an Angular component. The configuration object passed to the ng.core.Component() method has two fields, a selector and a template.

The selector specifies a simple CSS selector for a host HTML element named my-app. Angular creates and displays an instance of our AppComponent wherever it encounters a my-app element in the host HTML.

The template property holds the component's companion template. A template is a form of HTML that tells Angular how to render a view. Our template is a single line of HTML announcing "My First Angular App".

Now we need something to tell Angular to load this component.

Give it the boot

Add a new file , boot.js, to the app/ folder as follows:

We need two things to launch the application:

1. Angular's browser bootstrap function
2. The application root component that we just wrote.

We have them both in our 'namespaces'. Then we call bootstrap, passing in the root component type, AppComponent.

We've asked Angular to launch the app in a browser with our component at the root. Where will Angular put it?

Add the index.html

Angular displays our application in a specific location on our index.html. It's time to create that file.

We won't put our index.html in the app/ folder. We'll locate it up one level, in the project root folder.

Now create theindex.html file and paste the following lines:

There are three noteworthy sections of HTML:

1. We load the JavaScript libraries we need. angular2-polyfills.js and Rx.js are needed by Angular 2.
   

2. We load our JavaScript files, paying attention to their order (boot.js needs app.component.js to be there first).

3. We add the <my-app> tag in the <body>. This is where our app lives!

When Angular calls the bootstrap function in boot.js, it reads the AppComponent metadata, finds the my-app selector, locates an element tag named my-app, and loads our application between those tags.

Compile and run!

Open a terminal window and enter this command:

That command runs a static server called lite-server that loads index.html in a browser and refreshes the browser when application files change.

In a few moments, a browser tab should open and display

Congratulations! We are in business.

Make some changes

Try changing the message to "My SECOND Angular 2 app".

lite-server is watching, so it should detect the change, refresh the browser, and display the revised message.

It's a nifty way to develop an application!

We close the terminal window when we're done to terminate the server.

Final structure

Our final project folder structure looks like this:

And here are the files:

Wrap Up

Our first application doesn't do much. It's basically "Hello, World" for Angular 2.

We kept it simple in our first pass: we wrote a little Angular component, we added some JavaScript libraries to index.html, and launched with a static file server. That's about all we'd expect to do for a "Hello, World" app.

We have greater ambitions.

The good news is that the overhead of setup is (mostly) behind us. We'll probably only touch the package.json to update libraries. Besides adding in the script files for our app 'modules', we'll likely open index.html only if we need to add a library or some css stylesheets.

We're about to take the next step and build a small application that demonstrates the great things we can build with Angular 2.

Join us on the Tour of Heroes Tutorial!

Appendices

The balance of this chapter is a set of appendices that elaborate some of the points we covered quickly above.

There is no essential material here. Continued reading is for the curious.

Appendix: Browser ES6 support

Angular 2 relies on some ES2015 features, most of them found in modern browsers. Some browsers (including IE 11) require a shim to support the the needed functionality. Try loading the following shim above the other scripts in the index.html:

Appendix: package.json

npm is a popular package manager and Angular application developers rely on it to acquire and manage the libraries their apps require.

We specify the packages we need in an npm package.json file.

The Angular team suggests the packages listed in the dependencies and devDependencies sections listed in this file:

A package.json has an optional scripts section where we can define helpful commands to perform development and build tasks. We've included a number of such scripts in our suggested package.json:

We've seen how we can run the server with this command:

We are using the special npm start command, but all it does is run npm run lite.

We execute npm scripts in that manner: npm run + script-name. Here's what these scripts do:

• npm run lite - run the lite-server, a light-weight, static file server, written and maintained by John Papa with excellent support for Angular apps that use routing.

Appendix: Npm errors and warnings

All is well if there are no console messages starting with npm ERR! at the end of an npm install. There might be a few npm WARN messages along the way — and that is perfectly fine.

We often see an npm WARN message after a series of gyp ERR! messages. Ignore them. A package may try to re-compile itself using node-gyp. If the re-compile fails, the package recovers (typically with a pre-built version) and everything works.

We are in good shape as long as there are no npm ERR! messages at the very end of npm install.

Appendix: boot.js

Bootstrapping is platform-specific

We use the bootstrap function from ng.platform.browser, not ng.core. There's a good reason.

We only call "core" those capabilities that are the same across all platform targets. True, most Angular applications run only in a browser and we'll call the bootstrap function from this library most of the time. It's pretty "core" if we're always writing for a browser.

But it is possible to load a component in a different enviroment. We might load it on a mobile device with Apache Cordova We might wish to render the first page of our application on the server to improve launch performance or facilitate SEO.

These targets require a different kind of bootstrap function that we'd import from a different library.

Why do we create a separate boot.js file?

The boot.js file is tiny. This is just a QuickStart. We could have folded its few lines into the app.component.js file and spared ourselves some complexity.

We didn't for what we believe to be good reasons:

1. Doing it right is easy
2. Testability
3. Reusability
4. Separation of concerns
5. We learned about import and export

It's easy

Sure it's an extra step and an extra file. How hard is that in the scheme of things?

We'll see that a separate boot.js is beneficial for most apps even if it isn't critical for the QuickStart. Let's develop good habits now while the cost is low.

Testability

We should be thinking about testability from the beginning even if we know we'll never test the QuickStart.

It is difficult to unit test a component when there is a call to bootstrap in the same file. As soon as we load the component file to test the component, the bootstrap function tries to load the application in the browser. It throws an error because we're not expecting to run the entire application, just test the component.

Relocating the bootstrap function to boot.js eliminates this spurious error and leaves us with a clean component module file.

Reusability

We refactor, rename, and relocate files as our application evolves. We can't do any of those things while the file calls bootstrap. we can't move it. We can't reuse the component in another application. We can't pre-render the component on the server for better performance.

Separation of concerns

A component's responsibility is to present and manage a view.

Launching the application has nothing to do with view management. That's a separate concern. The friction we're encountering in testing and reuse stems from this unnecessary mix of responsibilities.

Import/Export

While writing a separate boot.js file we learned an essential Angular skill: how to 'export' from one 'module' and 'import' into another via our simple namespace abstraction. We'll do a lot of that as we learn more Angular.