2. The Hero Editor

Once Upon a Time

Every story starts somewhere. Our story starts where the QuickStart ends.

Run the live example for this part.

Create a folder called angular2-tour-of-heroes and follow the QuickStart steps which provide the prerequisites, the folder structure, and the core files for our Tour of Heroes.

We should have the following structure:

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

npm start

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.

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".

export class AppComponent {
  title = 'Tour of Heroes';
  hero = 'Windstorm';
}

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

template: '<h1>{{title}}</h1><h2>{{hero}} details!</h2>'

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.

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 a class.

Create a Hero class with id and name properties. For now put this near the top of the app.component.ts file, just below the import statement.

export class Hero {
  id: number;
  name: string;
}

Now that we have a Hero class, 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".

hero: Hero = {
  id: 1,
  name: 'Windstorm'
};

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.

template: '<h1>{{title}}</h1><h2>{{hero.name}} details!</h2>'

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.

template: '<h1>{{title}}</h1><h2>{{hero.name}} details!</h2><div><label>id: </label>{{hero.id}}</div><div><label>name: </label>{{hero.name}}</div>'

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.

template:`
  <h1>{{title}}</h1>
  <h2>{{hero.name}} details!</h2>
  <div><label>id: </label>{{hero.id}}</div>
  <div><label>name: </label>{{hero.name}}</div>
  `

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:

template:`
  <h1>{{title}}</h1>
  <h2>{{hero.name}} details!</h2>
  <div><label>id: </label>{{hero.id}}</div>
  <div>
    <label>name: </label>
    <input value="{{hero.name}}" placeholder="name">
  </div>
  `

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.

Before we can use two-way data binding for form inputs, we need to import the FormsModule package in our Angular module. We add it to the NgModule decorator's imports array. This array contains the list of external modules used by our application. Now we have included the forms package which includes ngModel.

import { NgModule }      from '@angular/core';
import { BrowserModule } from '@angular/platform-browser';
import { FormsModule }   from '@angular/forms';

import { AppComponent }  from './app.component';

@NgModule({
  imports: [
    BrowserModule,
    FormsModule
  ],
  declarations: [
    AppComponent
  ],
  bootstrap: [ AppComponent ]
})
export class AppModule { }

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

Replace the <input> with the following HTML

<input [(ngModel)]="hero.name" placeholder="name">

The browser refreshes. We see our hero again. We can edit the hero’s name and see the changes reflected immediately in the <h2>.

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 kind 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 this part.

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

import { Component } from '@angular/core';

export class Hero {
  id: number;
  name: string;
}

@Component({
  selector: 'my-app',
  template: `
    <h1>{{title}}</h1>
    <h2>{{hero.name}} details!</h2>
    <div><label>id: </label>{{hero.id}}</div>
    <div>
      <label>name: </label>
      <input [(ngModel)]="hero.name" placeholder="name">
    </div>
    `
})
export class AppComponent {
  title = 'Tour of Heroes';
  hero: Hero = {
    id: 1,
    name: 'Windstorm'
  };
}

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 a hero in the next tutorial chapter.