angular-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.

  [Run the live example for part 1](/resources/live-examples/toh-1/ts/plnkr.html)

  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:

.filetree
  .file angular2-tour-of-heroes
  .children
    .file node_modules
    .file app
    .children
      .file app.component.ts
      .file main.ts
    .file index.html
    .file package.json
    .file tsconfig.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 start

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

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

.l-sub-section
  :marked
    #### Interface or Class?
    Why a `Hero` interface and not a `Hero` class? 
    We want a strongly typed `Hero`. We get strong typing with either option. 
    Our choice depends on how we intend to use the `Hero`. 
    
    If we need a `Hero` that goes beyond simple properties, a `Hero` with logic and behavior, 
    we must define a class. 
    If we only need type checking, the interface is sufficient and lighter weight.
    
    Lighter weight? Transpiling a class to JavaScript produces code. 
    Transpiling an interface produces — nothing.
    If the class does nothing (and there is nothing for a `Hero` class to do right now),
    we prefer an interface.

: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-snippets/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-snippets/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-snippets/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-snippets/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-snippets/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 
    [Forms](../guide/forms.html#ngModel) and
    [Template Syntax](../guide/template-syntax.html#ngModel) chapters.
: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`.

  [Run the live example for part 1](/resources/live-examples/toh-1/ts/plnkr.html)

  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).