angular-docs-cn/public/docs/ts/latest/tutorial/toh-pt1.jade

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

:marked
  # Once Upon a Time

  Every story starts somewhere. Our story starts where the [QuickStart](../quickstart.html) ends.

  Follow the "QuickStart" steps. They provide the prerequisites, the folder structure,
  and the core files for our Tour of Heroes.

  Copy the "QuickStart" code to a new folder and rename the folder `angular2-tour-of-heroes`.
  We should have the following structure:

code-example(format="").
    angular2-tour-of-heroes
      ├── node_modules
      ├── app
      |    ├── app.component.ts
      |    └── boot.ts
      ├── index.html
      ├── tsconfig.json
      └── package.json

:marked
  ## Keep the app transpiling and running
  We want to start the TypeScript compiler, have it watch for changes, and start our server. We'll do this by typing

code-example(format="" language="bash").
  npm run go

:marked
  This command starts the server, launches the app in a browser,
  and keeps the app running while we continue to build the Tour of Heroes.

.l-sub-section
  :marked
    These two steps watch all project files. They recompile TypeScript files and re-run
    the app when any file changes.
    If the watchers fail to detect renamed or new files,
    stop these commands in each terminal by typing `CTRL+C` and then re-run them.
.l-main-section
  :marked
    ## Show our Hero
    We want to display Hero data in our app

    Let's add two properties to our `AppComponent`, a `title` property for the application name and a `hero` property
    for a hero named "Windstorm".

  +makeExample('toh-1/ts/app/app.component.snippets.pt1.ts', 'app-component-1', 'app.component.ts (AppComponent class)')(format=".")

  :marked
    Now we update the template in the `@Component` decoration with data bindings to these new properties.

  +makeExample('toh-1/ts/app/app.component.snippets.pt1.ts', 'show-hero')
  
  :marked
    The browser should refresh and display our title and hero.

    The double curly braces tell our app to read the `title` and `hero` properties from the component and render them.
    This is the "interpolation" form of one-way data binding.
.l-sub-section
  :marked
    Learn more about interpolation in the [Displaying Data chapter](../guide/displaying-data.html).
:marked
  ### Hero object

  At the moment, our hero is just a name.  Our hero needs more properties.
  Let's convert the `hero` from a literal string to an interface.

  Create a `Hero` interface with `id` and `name` properties.
  Keep this near the top of the `app.component.ts` file for now.

+makeExample('toh-1/ts/app/app.component.snippets.pt1.ts', 'hero-interface-1', 'app.component.ts (Hero interface)')(format=".")

.l-sub-section
  :marked
    Why an interface and not a class? The net result is that either option will allow us to check the types. The answer here lies in how we intend to use the Hero. We want something to check the types, so either option will suffice. If we wanted to create an instance of a Hero, a class may be more appropriate since we could add logic to a Hero constructor. But our scenario is for type checking, so the interface is adequate. The driving reason however, that leads us to a Hero interface is that the interface when transpiled from TypeScript to JavaScript produces no ES5 code. None at all. While a TypeScript class does generate ES5 code. For these reasons we choose an interface here.

:marked
  Now that we have a `Hero` interface, let’s refactor our component’s `hero` property to be of type `Hero`.
  Then initialize it with an id of `1` and the name, "Windstorm".

+makeExample('toh-1/ts/app/app.component.snippets.pt1.ts', 'hero-property-1', 'app.component.ts (Hero property)')(format=".")

:marked
  Because we changed the hero from a string to an object,
  we update the binding in the template to refer to the hero’s `name` property.

+makeExample('toh-1/ts/app/app.component.snippets.pt1.ts', 'show-hero-2')
:marked
  The browser refreshes and continues to display our hero’s name.

  ### Adding more HTML
  Displaying a name is good, but we want to see all of our hero’s properties.
  We’ll add a `<div>` for our hero’s `id` property and another `<div>` for our hero’s `name`.

+makeExample('toh-1/ts/app/app.component.snippets.pt1.ts', 'show-hero-properties')
:marked
  Uh oh, our template string is getting long. We better take care of that to avoid the risk of making a typo in the template.

  ### Multi-line template strings

  We could make a more readable template with string concatenation
  but that gets ugly fast, it is harder to read, and
  it is easy to make a spelling error. Instead,
  let’s take advantage of the template strings feature
  in ES2015 and TypeScript to maintain our sanity.

  Change the quotes around the template to back-ticks and
  put the `<h1>`, `<h2>` and `<div>` elements on their own lines.

+makeExample('toh-1/ts/app/app.component.snippets.pt1.ts', 'multi-line-strings', 'app.component.ts (AppComponent\'s template)')

  .callout.is-important
    header A back-tick is not a single quote
    :marked
      **Be careful!** A back-tick (`) looks a lot like a single quote (').
      It's actually a completely different character.
      Back-ticks can do more than demarcate a string.
      Here we use them in a limited way to spread the template over multiple lines.
      Everything between the back-ticks at the beginning and end of the template
      is part of a single template string.

.l-main-section
  :marked
    ## Editing Our Hero

    We want to be able to edit the hero name in a textbox.

    Refactor the hero name `<label>` with `<label>` and `<input>` elements as shown below:

  +makeExample('toh-1/ts/app/app.component.snippets.pt1.ts', 'editing-Hero', 'app.component.ts (input element)')
  :marked
    We see in the browser that the hero’s name does appear in the `<input>` textbox.
    But something doesn’t feel right.
    When we change the name, we notice that our change
    is not reflected in the `<h2>`. We won't get the desired behavior
    with a one-way binding to `<input>`.

    ### Two-Way Binding

    We intend to display the name of the hero in the `<input>`, change it,
    and see those changes wherever we bind to the hero’s name.
    In short, we want two-way data binding.

    Let’s update the template to use the  **`ngModel`** built-in directive for two-way binding.

  .l-sub-section
    :marked
      Learn more about `ngModel` in the [Template Syntax chapter](../guide/template-syntax.html#ng-model)
  :marked
    Replace the `<input>` with the following HTML

  code-example(language="html").
     &lt;input [(ngModel)]="hero.name" placeholder="name">

  :marked
    The browser refreshes. We see our hero again. We can edit the hero’s name and
    see the changes reflected immediately in the `<h2>`.
    
.l-main-section
  :marked
    ## The Road We’ve Travelled
    Let’s take stock of what we’ve built.

    * Our Tour of Heroes uses the double curly braces of interpolation (a form of one-way data binding)
    to display the application title and properties of a `Hero` object.
    * We wrote a multi-line template using ES2015’s template strings to make our template readable.
    * We can both display and change the hero’s name after adding a two-way data binding to the `<input>` element
    using the built-in `ngModel` directive.
    * The `ngModel` directive also propagates changes to every other binding of the `hero.name`.

    Here's the complete `app.component.ts` as it stands now:

  +makeExample('toh-1/ts/app/app.component.ts', 'pt1', 'app.component.ts')

.l-main-section
  :marked
    ## The Road Ahead
    Our Tour of Heroes only displays one hero and we really want to display a list of heroes.
    We also want to allow the user to select a hero and display their details.
    We’ll learn more about how to retrieve lists, bind them to the
    template, and allow a user to select it in the
    [next tutorial chapter](./toh-pt2.html).