angular-docs-cn/public/docs/js/latest/quickstart.jade

include _util-fns

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

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

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  ## See It Run!

  Running the [live example](/resources/live-examples/quickstart/js/plnkr.html)
  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](http://plnkr.co/ "Plunker"),
  and displays a simple message:

figure.image-display
  img(src='/resources/images/devguide/quickstart/my-first-app.png' alt="Output of quickstart app")
:marked
  Here is the file structure:
.filetree
  .file angular2-quickstart
  .children
    .file app
    .children
      .file app.component.js
      .file main.js
    .file index.html
    .file license.md
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  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
  1. Write the Angular root component for our app
  1. Bootstrap it to take control of the main web page
  1. Write the main page (`index.html`)
  
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  :marked
    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.
:marked

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  ## 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
  
code-example(format="").
  mkdir angular2-quickstart
  cd    angular2-quickstart
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  ### Add the libraries we need
  
  We recommend the **npm** package manager for acquiring and managing our development libraries.

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  :marked
    Don't have npm?
    [Get it now](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 this documentation.
:marked
  Add a **package.json** file to the project folder and copy/paste the following:
+makeJson('quickstart/js/package.1.json', null, 'package.json')(format=".")  

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  :marked
    Itching to know the details? We explain in the [appendix below](#package-json)  
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  Install these packages by opening a terminal window (command window in Windows) and
  running this npm command.
code-example(format="").
  npm install
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.l-sub-section
  :marked
    Scary <span style="color:red; font-weight: bold">error messages in red</span> may appear **during** install. 
    Ignore them. The install will succeed. See the [appendix below](#npm-errors) for more information.

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  ## 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.
code-example(format="").
  mkdir app
  cd    app
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  ### Add the component file
  Now add a file named **app.component.js** and paste the following lines:
+makeExample('quickstart/js/app/app.component.js', null, 'app/app.component.js')(format=".")
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  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`**.
  
+makeExample('quickstart/js/app/app.component.js', 'ng-namespace-funcs', 'app/app.component.js ' +
'(component schema)')(format=".")

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  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 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").
  
+makeExample('quickstart/js/app/app.component.js', 'iife', 'app/app.component.js (IIFE)')(format=".")
  
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  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`.
  
+makeExample('quickstart/js/app/app.component.js', 'export', 'app/app.component.js (export)')(format=".")
  
:marked
  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:
    
+makeExample('quickstart/js/app/main.js', 'import','app/main.js (import)')(format=".")

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  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.
  
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  ### 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.
  
+makeExample('quickstart/js/app/app.component.js', 'class','app.component.js (class)')(format=".")  
  
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  ### 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`.
  
+makeExample('quickstart/js/app/app.component.js', 'component','app.component.js (component)')(format=".")    

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  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.
  
.alert.is-helpful
  :marked
    Remember the `my-app` selector! We'll need that information when we write our `index.html`
:marked
  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 2 App".
  
  Now we need something to tell Angular to load this component.

  ### Bootstrap it!
  
  Add a new file , `main.js`, to the `app/` folder as follows:
+makeExample('quickstart/js/app/main.js', null, 'app/main.js')(format=".")
:marked
  We need two things to launch the application:
  1. Angular's browser `bootstrap` function
  1. 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`.
 
.l-sub-section
  :marked
    Learn why we need `bootstrap` from `ng.platformBrowserDynamic`
    and why we create a separate *main.js* file in the [appendix below](#main).
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  We've asked Angular to launch the app in a browser with our component at the root.
  Where will Angular put it? 

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  ## 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**.
  
code-example(format="").
  cd ..
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  Now create the`index.html` file and paste the following lines:
+makeExample('quickstart/js/index.html', null, 'index.html')(format=".")
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  There are three noteworthy sections of HTML:

  1. We load the JavaScript libraries we need; learn about them [below](#libraries).

  2. We load our JavaScript files, paying attention to their order (`main.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 `main.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.

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:marked
  ## Run!
  
  Open a terminal window and enter this command:
code-example(format="").
  npm start
:marked
  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

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

:marked
  Congratulations!  We are in business.

.alert.is-helpful
  :marked
    If you see `Loading...` displayed instead, see the
    [Browser ES2015 support appendix](#es6support).
:marked
  ### 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.

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:marked
  ## Final structure
  Our final project folder structure looks like this:
.filetree
  .file angular2-quickstart
  .children
    .file node_modules
    .file app
    .children
      .file app.component.js
      .file main.js
    .file index.html
    .file package.json
:marked
  And here are the files:
+makeTabs(`
    quickstart/js/app/app.component.js,
    quickstart/js/app/main.js,
    quickstart/js/index.html,
    quickstart/js/package.1.json
  `,null,
  `app/app.component.js, app/main.js, index.html,package.json`)
:marked

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:marked
  ## 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](./tutorial)!


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  ## 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.

<a id="ie-polyfills"></a>
<a id="es6support"></a>
<a id="libraries"></a>
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:marked
  ### Appendix: Libraries
  We loaded the following scripts
+makeExample('quickstart/js/index.html', 'libraries', 'index.html')(format=".")
:marked
  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 Angular2, `zone.js` and `Reflect.js`,
  followed by the Reactive Extensions RxJS library.
.l-sub-section
  :marked
    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.
:marked
  Finally, we loaded the web development version of Angular 2 itself.

  We'll make different choices as we gain experience and
  become more concerned about production qualities such as
  load times and memory footprint.  
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:marked


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:marked
  <a id="package-json"></a>
  ### Appendix: package.json

  [npm](https://docs.npmjs.com/) 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](https://docs.npmjs.com/files/package.json) file.
  
  The Angular team suggests the packages listed in the `dependencies` and `devDependencies`
  sections listed in this file:

+makeJson('quickstart/js/package.1.json',{ paths: 'dependencies, devDependencies'}, 'package.json (dependencies)')(format=".") 
:marked
.l-sub-section
  :marked
    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.
:marked
  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`:
+makeJson('quickstart/js/package.1.json',{ paths: 'scripts'}, 'package.json (scripts)')(format=".") 
:marked
  We've seen how we can run the server with this command:
code-example(format="").
  npm start
:marked
  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](https://www.npmjs.com/package/lite-server), 
  a light-weight, static file server, written and maintained by [John Papa](http://johnpapa.net/) 
  with excellent support for Angular apps that use routing.


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  <a id="npm-errors"></a>
  ### 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 &mdash; 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`.
  
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  <a id="main"></a>
  ### Appendix: ***main.js***

  #### Bootstrapping is platform-specific
  We use the `bootstrap` 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 enviroment. 
  We might load it on a mobile device with [Apache Cordova](https://cordova.apache.org/) or [NativeScript](https://www.nativescript.org/).
  We might wish to render the first page of our application on the server 
  to improve launch performance or facilitate 
  [SEO](http://www.google.com/webmasters/docs/search-engine-optimization-starter-guide.pdf).

  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*** file?
  
  The *main.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
  1. Testability
  1. Reusability
  1. Separation of concerns
  1. 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` 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 `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 `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 `main.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.