Let's start from zero and build a super simple Angular application in JavaScript.
Although we're getting started in JavaScript, you can also write Angular apps in TypeScript by selecting it from the combo-box in the banner.
See It Run!
Running the
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
, styles.css
and three 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.
- Set up our development environment
- Write the Angular root component for our app
- Add an Angular Module
- Bootstrap it to take control of the main web page
- Write the main page (
index.html
) - Add some CSS (
styles.css
)
We really can build the QuickStart from scratch in five minutes if we follow the instructions and ignore the commentary.
Most of us will be interested in the "why" as well as the "how" and that will take longer.
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.
Don't have npm? Get it now because we're going to use it now and repeatedly throughout this documentation.
Add a package.json file to the project folder and copy/paste the following:
package.json
Itching to know the details? We explain in the appendix below
Install these packages by opening a terminal window (command window in Windows) and running this npm command.
Scary error messages in red may appear during install. Ignore them. The install will succeed. See the appendix below for more information.
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 src/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:
src/app/app.component.js
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
.
src/app/app.component.js (component schema)
The Component
method takes a configuration object with three
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 a native module system. There are several popular 3rd party module systems we could use. Instead, for simplicity and to avoid picking favorites, we'll create a single global namespace for our application.
We'll call it app
and we'll add all of our code artifacts to this one global object.
We don't want to pollute the global namespace with anything else. So within each file we surround the code in an IIFE ("Immediately Invoked Function Expression").
src/app/app.component.js (IIFE)
We pass the global app
namespace object into the IIFE,
taking care to initialize it with an empty object if it doesn't yet exist.
Most application files export one thing by adding that thing to the app
namespace.
Our app.component.js
file exports the AppComponent
.
src/app/app.component.js (export)
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:
src/app/app.module.js (import)
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.
app.component.js (class)
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
.
app.component.js (component)
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.
Remember the my-app
selector! We'll need that information when we write our index.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 "Hello Angular".
Now we need something to tell Angular to load this component.
Add an NgModule
Angular apps are composed of Angular Modules that snuggly contain all our components and everything else we need for our app.
Create the src/app/app.module.js
file with the following content:
src/app/app.module.js
Read more about the NgModule
configuration in the appendix below.
Bootstrap it!
Add a new file , main.js
, to the src/app/
folder as follows:
src/main.js
We need two things to launch the application:
- Angular's
platformBrowserDynamic().bootstrapModule
function - The application root module that we just wrote.
We have them both in our 'namespaces'.
Then we call bootstrapModule
, passing in the root app module, AppModule
.
Learn why we need bootstrapModule
from ng.platformBrowserDynamic
and why we create a separate js files in the appendix below.
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 src/app/
folder.
We'll locate it up one level, in the project root folder.
Now create theindex.html
file and paste the following lines:
src/index.html
There are three noteworthy sections of HTML:
We load the JavaScript libraries we need; learn about them below.
We load our JavaScript files.
We add the
<my-app>
tag in the<body>
. This is where our app lives!
When Angular calls the bootstrapModule
function in main.js
,
it reads the AppModule
metadata, sees that AppComponent
is the bootstrap component,
finds the my-app
selector, locates an element tag named my-app
,
and renders our application's view between those tags.
Add some style
Styles aren't essential but they're nice, and index.html
assumes we have
a stylesheet called styles.css
.
Create a styles.css
file in the project root folder and start styling, perhaps with the minimal
styles shown below. For the full set of master styles used by the documentation samples,
see styles.css.
src/styles.css
Configure the server
We're going to use a static server called lite-server that loads index.html
in a browser
and refreshes the browser when application files change.
The static server will use the bs-config.json
file as configuration.
This files tells the server that src/
is the base directory to serve, and that any
requests to node_modules/
should be routed to node_modules/
in the root directory
instead of src/node_modules/
Run!
Open a terminal window and enter this command:
That command runs lite-server.
In a few moments, a browser tab should open and display
Congratulations! We are in business.
If you see Loading...
displayed instead, see the
Browser ES2015 support appendix.
Make some changes
Try changing the message to "Hello Angular!".
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.
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.
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: Libraries
We loaded the following scripts
src/index.html
We began with an Internet Explorer polyfill. IE requires a polyfill to run an application that relies on ES2015 promises and dynamic module loading. Most applications need those capabilities and most applications should run in Internet Explorer.
Next are the polyfills for Angular, zone.js
and Reflect.js
,
followed by the Reactive Extensions RxJS library.
Our QuickStart doesn't use the Reactive Extensions but any substantial application will want them when working with observables. We added the library here in QuickStart so we don't forget later.
Finally, we loaded the web development version of Angular itself.
We'll make different choices as we gain experience and become more concerned about production qualities such as load times and memory footprint.
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:
package.json (dependencies)
There are other possible package choices. We're recommending this particular set that we know work well together. Play along with us for now. Feel free to make substitutions later to suit your tastes and experience.
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
:
package.json (scripts)
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 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.
Just make sure there are no npm ERR!
messages at the very end of npm install
.
Appendix: NgModule
The NgModule
decorator is listing:
- What other Angular Modules ours uses
- Which components and directives we declare in our components
- The component to bootstrap at the start
We import our lone app.AppComponent
and add it to both declarations
and bootstrap
array.
Notice that we also add ng.platformBrowser.BrowserModule
to the imports
array.
This is the Angular Module that contains all the needed Angular bits and pieces to run our app in the browser.
Angular itself is split into separate Angular Modules so we only need to import the ones we really use.
One of the most common ones is FormsModule
, and soon we'll also see RouterModule
and HttpModule
.
Appendix: main.js
Bootstrapping is platform-specific
We use the platformBrowserDynamic().bootstrapModule
function from ng.platformBrowserDynamic
,
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 environment. We might load it on a mobile device with Apache Cordova or NativeScript. 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 main.js, app.module.js and app.component.js files?
The main.js file is tiny. This is just a QuickStart.
We could have folded its few lines into the app.module.js
file, and that one into
app.component.js
and spared ourselves some complexity.
We didn't for what we believe to be good reasons:
- Doing it right is easy
- Testability
- Reusability
- Separation of concerns
- 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 main.js
and app.module.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 bootstrapModule
in the same file.
As soon as we load the component file to test the component,
the bootstrapModule
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 bootstrapModule
function to main.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 bootstrapModule
.
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, and a NgModule's reponsibility is to define the application context.
Launching the application has nothing to do with any of these. 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 main.js
and app.module.js
files 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.