include ../../../../_includes/_util-fns

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

.callout.is-helpful
  header Don't want TypeScript?
  :markdown
    Although we're getting started in TypeScript, you can also write Angular 2 apps
    in JavaScript and Dart by selecting either of those languages from the combo-box in the banner.

.l-main-section

  :markdown
    # The shortest, quickest ...

    Let's put something on the screen in Angular 2 as quickly as we can.

  .l-sub-section
    :markdown
      While we are about to describe steps to take on your development machine,
      you could take these same steps in an interactive, online coding environment
      such as [plunker](http://plnkr.co/ "Plunker"). You won't have to
      install a static server to run the app there.

      If you like what you see - and we think you will - you can repeat this
      exercise on your own machine later.

  :markdown
    **Create a new folder** to hold our application project, perhaps like this:
    ```
    mkdir angular2-getting-started
    cd    angular2-getting-started
    ```

    ## Our first Angular component

    **Add a new file** called **`app.ts`** and paste the following lines:

  +makeExample('gettingstarted/ts/src/app/app.ts', null, 'app.ts')

  :markdown
    We've just defined an Angular 2 **component**,
    one of the most important Angular 2 features.
    Components are our primary means of creating application views
    and supporting them with application logic.

    Ours is an empty, do-nothing class class named `AppComponent`.
    It would expand with properties and application
    logic when we're ready to build a substantive application.

    Above the class we see the `@Component` decoration.

  .l-sub-section
    :markdown
      The `@` symbol before the method name identifies `Component` as a decoration.
      A "decoration" is a TypeScript language feature
      for creating metadata about the class. Angular finds this metadata
      in the transpiled JavaScript and responds appropriately.
  :markdown
    `@Component` tells Angular that this class *is an Angular component*.
    The configuration object passed to the `@Component` method has two
    field, a `selector` and a `template`.

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

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

    The `bootstrap` method tells Angular to start the application with this
    component at the application root.
    We'd be correct to guess that someday our application will
    consist of more components arising in tree-like fashion from this root.

    In the top line we imported the `Component`, `View`, and `bootstrap` methods
    from the Angular 2 library. That's the way we do things now.
    We no longer expect to find our code or any library code in a global namespace.
    We `import` exactly what we need, as we need it, from named file and library resources.

    ## Add `index.html`

    **Create** an `index.html` file.

    **Paste** the following lines into it ... and we'll discuss them:

  +makeExample('gettingstarted/ts/src/index.1.html', null, 'index.html')

  :markdown
    We see three noteworthy sections of HTML:

    1. We load JavaScript libraries from the web.
    Let's take them on faith without further discussion.<br/><br/>

    2. We configure something called `System` and ask it to import the
    application file with our `AppComponent` that we just wrote.
    `System` is the module loader (from the `system.js` library),
    a tool that can `import` code;
    remember the `import` statement in our `AppComponent`?

      We're also asking `system.js` to "transpile" (AKA "compile") our
      TypeScript source code into JavaScript ... right here in the browser.<br/><br/>

    3. We note the `<my-app>` tag in the `<body>`.
    That's the custom HTML element we identified in the `@Component` decoration
    adorning our `AppComponent` class.

    ## Run it!

    We need a static file server to serve our application to the browser.

  .l-sub-section
    :markdown
      Don't have a static file server handy?  Let's install one of our favorites
      called [live-server](https://www.npmjs.com/package/live-server "Live-server").

      We'll use the **npm package manager** to install it. Don't have npm?
      [Go get it](https://docs.npmjs.com/getting-started/installing-node "Installing Node.js and updating npm")
      because we're going to use it now and repeatedly throughout the guide.

      Once you have `npm` installed, open a terminal window and enter

    pre.prettyprint.lang-bash
      code npm install -g live-server

  :markdown
    Open a terminal window and enter

  pre.prettyprint.lang-bash
      code live-server
  :markdown
    In a few moments, a browser tab should open and display

  figure.image-display
    img(src='/resources/images/devguide/getting-started/my-first-app.png' alt="Output of getting started app")

  :markdown
    Congratulations!  We are in business.

.l-main-section

  :markdown
    ## What's wrong with this?

    We were up and running in a hurry and we could explore Angular
    in this manner for quite some time.

    For a number of reasons this isn't a good approach for building an application.
    <!-- TODO The formatting here is a little weird. Should improve readability. -->

    * Transpiling TypeScript in the browser becomes tediously slow when our
    app grows beyond a few files. We certainly won't do that in production. We should learn to
    compile locally and push the generated JavaScript to the server. We'll need some tools for that.


    * We are writing TypeScript because we want strong-typing and some information
    about the APIs we're using. If we wrote `AppComponent` in a TypeScript-aware editor,
    we saw lots of red squiggly lines complaining about our code and
    we received no guidance about what `Component`, `View`, and `bootstrap` can do.
    We'll want to load TypeScript definition files to improve our coding experience.


    * Downloading JavaScript libraries from the web is OK for demos but
    it slows our development. Every time our app reloads, it must refetch these libraries.
    Don't count on browser caching.
    Our debugging and live-reload techniques will bust the browser cache. Loading libraries
    from the web also prevents us from developing our application offline or where connectivity is
    poor. Let's learn to download the libraries to our machine and serve them locally.


    * We want our development cycle to be as fast and friction-free as possible.
    When we change our code, we want to see the results in the browser immediately.
    We have tools and procedures for that.

.l-main-section

  :markdown
    # Upping our game
      Let's take a few more steps to put our development on a better foundation. We will

      1. Revise the application project structure for future growth
      1. Install a few tools and packages
      1. Prepare for local TypeScript compilation
      1. Revise the **`index.html`** to use local library resources
      1. Compile the TypeScript locally and watch for changes

    Shut down the `live-server` running in the terminal window (Ctrl-C) and proceed as follows.

.l-main-section
  :markdown
    ## Revise the application project structure

    At the moment we're dumping everything into the "angular2-getting-started" **root folder**.
    Not bad when there are only two files. Not good as our application evolves.

    Let's give our project a little structure.

    We'll add a sub-folder - `src` - to hold project source code and a sub-sub-folder - `src/app` -
    to hold the application source code.

    In OS/X and Linux:

  pre.prettyprint.lang-bash
    code mkdir src/app

  :markdown
    In Windows:

  pre.prettyprint.lang-bash
    code mkdir src\app

  :markdown
    **Move `index.html`** into the **`src`** folder.

    **Move `app.ts`** into the **`src/app`** folder.

    Our project folders should look like this.
    ```
    angular2-getting-started
    └── src
        ├── app
        │   └── app.ts
        └── index.html
    ```

.l-main-section

  :markdown
    ## Install npm packages locally

    We'll replace the web-based scripts in our `index.html` with
    scripts resident on our local machine.
    We get those scripts by installing two runtime `npm` packages into our project.

    >**angular.js** - the Angular 2 library.

    >**system.js** - an open-source library that provides module loading.

    We'll also install three development tools:

    >**typescript** - the TypeScript compiler

    >**tsd** - the [tsd package manager](https://www.npmjs.com/package/tsd "TSD Package Manager") so we can access
    [TypeScript type definition files](http://definitelytyped.org/ "Definitely Typed")

    >**[live-server](https://www.npmjs.com/package/live-server "Live-server")** - the static file server that reloads the browser when files change.
    We may have loaded it earlier. We're doing it again
    locally in our project so we are no longer vulnerable to
    a global uninstall or version change.

    **Open** a terminal window at our application's **root folder**

    Enter these commands:
    ```
    npm init -y
    npm i angular2@2.0.0-alpha.39 systemjs@0.19.2 --save --save-exact
    npm i typescript tsd live-server --save-dev
    ```

    These commands both *install* the packages and *create* an npm `package.json` that will
    help us develop and maintain our application in future.
    The essence of our `package.json` should look like this:

  +makeJson('gettingstarted/ts/package.json', { paths: 'name, version, dependencies, devDependencies'})

  :markdown
    There is also a `scripts` section. **Find and replace** it with the following:

  +makeJson('gettingstarted/ts/package.json', { paths: 'scripts'})

  :markdown
    We've just extended our project world with script commands
    that we'll be running very soon.

.l-main-section
  :markdown
    ## Update `index.html`

    **Replace** the library scripts section with references to
    scripts in the packages we just installed.

  +makeExample('gettingstarted/ts/src/index.html', 'libraries')

  :markdown
    **Update** the `System` configuration script as follows.

  +makeExample('gettingstarted/ts/src/index.html', 'systemjs')

  .l-sub-section
    :markdown
      We won't be transpiling TypeScript in the browser anymore.
      We'll do that on our machine and ship the generated JavaScript
      files to the server.

      We have to re-configure `system.js` to expect JavaScript files
      with a `.js` extension by default.
      Someday we might add a `Foo` class to our application in a `foo.ts`
      file and import it like this

    pre.prettyprint.lang-bash
      code import {Foo} from './app/foo'
    :markdown
       `system.js`will know to look for a file named `foo.js` in the `src/app` folder.

       That's exactly what we're doing in the last line. We're
       importing our main application file `app` (the generated `app.js` to be precise)
       from the `src/app/` folder (we moved it there, remember?)
  :markdown
    Here's the final version

  +makeExample('gettingstarted/ts/src/index.html', null, 'index.html')

.l-main-section
  :markdown
    ## Prepare for TypeScript Compilation

    ### Add links to TypeScript definition files

    We prefer writing TypeScript apps in editors that understand TypeScript,
    such as [Visual Studio Code](https://code.visualstudio.com/) and
    [Web Storm](https://www.jetbrains.com/webstorm/features/).
    Such editors improve the development experience by checking type information and
    displaying API documentation ("intellisense") based on TypeScript definition files (`.d.ts`).

    The definition files we need are included in the npm packages we just installed.
    We'll use the
    [**tsd package manager**](https://www.npmjs.com/package/tsd "TSD Package Manager")
    to generate an *aggregate TypeScript definition file*, **`tsd.d.ts`**,
    that holds links to the type definition files in those packages.

    In the ***root* folder** enter the following command
    (one of the `npm` scripts we added a short while ago)

  pre.prettyprint.lang-bash
    code npm run tsd

  :markdown
    That produces a new **`src/typings`** folder with the **`tsd.d.ts`** file.

    Now type-checking and intellisense light up automatically as we write our app
    in the Visual Studio Code and Web Storm editors. Check your editor's documentation for
    instructions on using the `tsd.d.ts` file.

    ### Add the TypeScript configuration file

    We'll add a configuration file named **`tsconfig.json`**
    to tell the editor how to interpret our TypeScript code and
    to simplify the TypeScript compilation command that we'll run very soon.

    **Change to the `src` folder and create a `tsconfig.json`** file with the following content:
  +makeJson('gettingstarted/ts/src/tsconfig.json', null, 'tsconfig.json')

  .alert.is-helpful
    :markdown
      When the `noImplicitAny` flag is `true`, the compiler demands that we supply type information
      unless the compiler can infer the type. It won't allow an identifier to default to the `any` type.
      This setting is a preference, not a mandate.

      Many of us prefer `noImplicitAny` because we want the TypeScript compiler to enforce type-safety vigorously.
      That's one of the reasons we are writing our app in TypeScript.
      Other people set this flag to `false` because they prefer more relaxed type checking.
      Folks new to TypeScript are sometimes overwhelmed by the rigor;
      they too may set the flag to `false` .. while they learn.

.l-main-section
  :markdown
    ## Final structure
    Our final project folder structure should look like this:
    ```
    angular2-getting-started
    ├── node_modules
    ├── src
    │    ├── app
    |    │    └── app.ts
    │    ├── typings
    │    │    └──tsd.d.ts
    │    ├── index.html
    │    └── tsconfig.json
    └── package.json
    ```

.l-main-section
  :markdown
    ## Compile the TypeScript to JavaScript

    We no longer transpile TypeScript to JavaScript in the browser.
    We run the **T**ype**S**cript **C**ompiler (TSC) on our machine instead.

    Open a terminal window in the **root of the application folder** and enter:

  pre.prettyprint.lang-bash
    code npm run tsc

  :markdown
    When it's done we should find the generated *app.js* file in the *src* folder and also an *app.map.js* file that
    helps debuggers navigate between the JavaScript and the TypeScript source.

    Our script set the compiler watch option (`-w`) so the
    compiler stays alive when it's finished.
    It watches for changes to our **`.ts`** files
    and recompiles them automatically.

    Leave this command running in the terminal window.
    You can stop it anytime with `Ctrl-C`.

.l-main-section
  :markdown
    ## Run the app!

    Now we are ready to see our app in action.

    Open another terminal window in the **root of the application folder** and
    launch `live-server` again although this time we'll do it with
    one of our `npm` script commands:

  pre.prettyprint.lang-bash
    code npm start

  :markdown
    **live-server** loads the browser for us, serves the HTML and JavaScript files,
    and displays our application message once more:

  figure.image-display
    img(src='/resources/images/devguide/getting-started/my-first-app.png' alt="Output of getting started app")

  :markdown
    ### Make some changes
    **`live-server`** detects changes to our files and refreshes the browser page for us automatically.

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

    The TypeScript compiler in the first terminal window is watching our source code. It recompiles and produces
    the revised *app.js*.  The `live-server` sees that change and reloads the browser.

    Keep `live-server` running in this terminal window. You can stop it anytime with `Ctrl-C`.

.l-main-section
  :markdown
    ## What have we done?
    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.**

    We won't ask Angular to build "Hello, World".
    We are asking it to help us build sophisticated applications with sophisticated requirements.

    So we made some strategic technology investments to reach our larger goals

    * our application loads faster with libraries installed locally and
    we can develop offline if we wish.

    * we added TypeScript definition files to enhance team
    productivity and code maintainability.

    * we're pre-compiling our TypeScript.

    * we're running the compiler and live-server with commands that give us immediate feedback as we make changes.

    The good news is that the overhead of setup is (mostly) behind us.
    We're about to build a small application that demonstrates the great things
    we can build with Angular 2.

    <!--TODO  Join us next on the [Tour of Heroes]. -->
