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(docs) overhaul user-input

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Ward Bell 2015-10-19 20:14:51 -07:00 committed by Naomi Black
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public/docs/ts/latest/guide/_data.json
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@ -16,7 +16,7 @@
"user-input": {
"title": "User Input",
"intro": "DOM events drive user input in Angular. You can use the native events like click, mouseover, and keyup. Angular uses a special syntax to register events to DOM elements. This section covers all the ins and outs of using the event syntax."
"intro": "User input triggers DOM events. We listen to those events with EventBindings that funnel updated values back into our components and models."
},
"pipes": {

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public/docs/ts/latest/guide/template-syntax.jade
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@ -30,7 +30,7 @@ include ../../../../_includes/_util-fns
>[* and <template>](#star-template)
>[Local variables](#local-vars)
>[Local template variables](#local-vars)
>[Input and Output Properties](#inputs-outputs)
@ -124,7 +124,7 @@ code-example(format="" language="html" escape="html").
The component itself is usually the expression *context* in which case
the template expression usually references that component.
The expression context may include an object other than the component.
A [template local variable](#local-vars) is one such supplemental context object;
A [local template variable](#local-vars) is one such supplemental context object;
we’ll discuss that option below.
Another is the **`$event`** variable that contains information about an event raised on an element;

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.l-main-section
h2#section-responding-to-user-input Responding to user input with event syntax
:markdown
When the user clicks a link, pushes a button, or types on the keyboard
we want to know about it. These user actions all raise DOM events.
In this chapter we learn to bind to those events using the Angular Event Binding syntax.
p.
You can make your application respond to user input by using the event syntax. The event syntax starts with an event name surrounded by parenthesis: <code>(event)</code>. A controller function is then assigned to the event name: <code>(event)="controllerFn()"</code>.
p.
For a particular control like an input you can have it call methods on your controller on keyup event like so:
:markdown
## Binding to User Input Events
code-example(language="html").
&lt;input (keyup)="myControllerMethod()"&gt;
We can listen to [any DOM event](https://developer.mozilla.org/en-US/docs/Web/Events)
with an [Angular Event Binding](./template-syntax.html#event-binding).
h3#local-variables Local variables
p.
As in previous examples, you can make element references available to other parts of the template as a local
variable using the <code>#var</code> syntax. With this and events, we can do the old "update text as you type" example:
The syntax is simple. We assign a template expression to the DOM event name, surrounded in parentheses.
A click Event Binding makes for a quick illustration.
code-example(language="html").
&lt;input #myname (keyup)&gt;
&lt;p&gt;{{myname.value}}&lt;/p&gt;
code-example(language="html" ).
&lt;button (click)="onClickMe()">Click me&lt;/button>
:markdown
The `(click)` to the left of the equal sign identifies the button's click event as the **target of the binding**.
The text within quotes on the right is the "**template expression**" in which we
respond to the click event by calling the component's `onClickMe` method. A [template expression](./template-syntax.html#template-expressions) is a subset
of JavaScript with a few added tricks.
p.text-body(ng-non-bindable).
The <code>#myname</code> creates a local variable in the template that we'll refer to below in the
<code>&lt;p&gt;</code> element. The <code>(keyup)</code> tells Angular to trigger updates when it gets a keyup
event. And the <code>{{myname.value}}</code> binds the text node of the <code>&lt;p&gt;</code> element to the
input's value property.
p Let's do something a little more complex where users enter items and add them to a list like this:
figure.image-display
img(src='/resources/images/examples/user-input-example1.png' alt="Example of Todo App")
.l-ain-section
h2#section-create-an-array-property Create an array property
p.
With the default bootstrapping in place, create a controller class that will manage interactions with the
list. Inside the controller, add an array with an initial list of items. Then add a method that pushes new items
on the array when called.
code-tabs
code-pane(language="javascript" name="TypeScript" format="linenums").
//TypeScript
class TodoList {
todos: Array&lt;string&gt;;
constructor() {
this.todos = ["Eat Breakfast", "Walk Dog", "Breathe"];
}
addTodo(todo: string) {
this.todos.push(todo);
When writing a binding we must be aware of a template expression's **execution context**.
The identifers appearing within an expression belong to a specific context object.
That object is usually the Angular component that controls the template ... which it definitely is
in this case because that snippet of HTML belongs to the following component:
<!--
These sample can be found in http://plnkr.co/edit/mr63T5
-->
```
@Component({
selector: 'click-me',
template: '<button (click)="onClickMe()">Click me</button>'
})
class ClickMeComponent {
onClickMe(){
alert('You are my hero!')
}
}
code-pane(language="javascript" name="ES5" format="linenums").
//ES5
function TodoList() {
this.todos = ["Eat Breakfast", "Walk Dog", "Breathe"];
this.addTodo = function(todo) {
this.todos.push(todo);
};
}
.callout.is-helpful
header Production Best Practice
p.
As with the previous example, in a production application you will separate your model out into another class
and inject it into <code>TodoList</code>. We've omitted it here for brevity.
```
The `onClickMe` in the template refers to the `onClickMe` method of the component.
When the user clicks the button, Angular calls the component's `onClickMe` method.
.l-main-section
h2#section-display-the-list-of-todos Display the list of todos
p.
Using the <code>*ng-for</code> iterator, create an <code>&lt;li&gt;</code> for each item in the todos array and set
its text to the value.
:markdown
## Get user input from the $event object
We can bind to all kinds of events. Let's bind to the "keyup" event of an input box and replay
what the user types back onto the screen.
code-example(language="html" format="linenums").
&lt;ul&gt;
&lt;li *ng-for=&quot;#todo of todos&quot;&gt;
{{ todo }}
&lt;/li&gt;
&lt;/ul&gt;
.l-main-section
h2#section-add-todos-to-the-list Add todos to the list via button click
p.
Now, add a text input and a button for users to add items to the list. As you saw above, you can create a local
variable reference in your template with <code>#varname</code>. Call it <code>#todotext</code> here.
code-example(language="html" format="linenums").
&lt;input #todotext&gt;
p.
Lastly, specify the target of the click event binding as your controller's <code>addTodo()</code> method and pass
it the value. Since you created a reference called <code>todotext</code>, you can get the value with
<code>todotext.value.</code>
code-example(language="html" format="linenums").
&lt;button (click)="addTodo(todotext.value)"&gt;Add Todo&lt;/button&gt;
p And then create the <code>doneTyping()</code> method on TodoList and handle adding the todo text.
code-example(language="javascript" format="linenums").
doneTyping($event) {
if($event.which === 13) {
this.addTodo($event.target.value);
$event.target.value = null;
This time we'll both listen to an event and grab the user's input.
code-example(format="linenums" language="html" ).
@Component({
selector: 'key-up',
template: `
&lt;h4>Give me some keys!&lt;/h4>
&lt;div>&lt;input (keyup)="onKey($event)">&lt;div>
&lt;div>{{values}}&lt;/div>
`
})
class KeyUpComponent {
values='';
onKey(event) {
this.values += event.target.value + ' | ';
}
}
.l-main-section
h2#section-final-code Final Code
:markdown
Angular makes an event object available in the **`$event`** variable. The user data we want is in that variable somewhere.
code-tabs
code-pane(language="javascript" name="TypeScript" format="linenums").
//TypeScript
import {Component, View, bootstrap, NgFor, NgIf} from 'angular2/angular2';
The shape of the `$event` object is determined by whatever raises the event.
The `keyup` event comes from the DOM so `$event` must be a [standard DOM event object](https://developer.mozilla.org/en-US/docs/Web/API/Event).
The `$event.target` gives us the
[`HTMLInputElement`](https://developer.mozilla.org/en-US/docs/Web/API/HTMLInputElement) which
has a `value` property and that's where we find our user input data.
With had this in mind when we passed `$event` to our `onKey()` component method. That method extracts the user's input and
concatenates it to the previous user data that we're accumulating in the component's' `values` property.
We then use [interpolation](./template-syntax.html#interpolation)
to display the `values` property back on screen.
Enter the letters "abcd", backspace to remove them, and we should see:
code-example().
a | ab | abc | abcd | abc | ab | a | |
:markdown
.l-main-section
:markdown
## Get user input from a local template variable
There's another way to get the user data without the `$event` variable.
Angular has syntax feature called [**local template variables**](./template-syntax.html#local-vars).
These variables grant us direct access to an element.
We declare a local template variable by preceding an identifier with a hash/pound character (#).
Let's demonstrate with a clever keystroke loopback in a single line of template HTML.
We don't actually need a dedicated component to do this but we'll make one anyway.
code-example(format="linenums" language="html" ).
@Component({
selector: 'loop-back',
template: `&lt;input #box (keyup)="0"> &lt;p>{{box.value}}&lt;/p>`
})
class LoopbackComponent {
}
:markdown
We've declared a template local variable named `box` on the `<input>` element.
The `box` variable is a reference to the `<input>` element itself which means we can
grab the input element's `value` and display it
with interpolation between `<p>` tags. The display updates as we type. *Voila!*
**This won't work at all unless we bind to an event**. Angular only updates the bindings
(and therefore the screen)
if we do something in response to asynchronous events such as keystrokes.
In this silly example we aren't really interested in the event at all.
But an Event Binding requires a template expression to evaluate when the event fires.
Many things qualify as expressions, none simpler than a one-character literal
like the number zero. That's all it takes to keep Angular happy. We said it would be clever!
That local template variable is intriguing. It's clearly easer to get to the textbox with that
variable than to go through the `$event` object. Maybe we can re-write our previous
example using the variable to acquire the user's' input. Let's give it a try.
code-example(format="linenums" language="html" ).
@Component({
selector: 'key-up2',
template: `
&lt;h4>Give me some more keys!&lt;/h4>
&lt;div>&lt;input #box (keyup)="onKey(box.value)">&lt;div>
&lt;div>{{values}}&lt;/div>
`
})
class KeyUpComponentV2 {
values='';
onKey(value) {
this.values += value + ' | ';
}
}
:markdown
That sure seems easier.
An especially nice aspect of this approach is that our component code gets clean data values from the view.
It no longer requires knowledge of the `$event` and its structure.
.l-main-section
:markdown
## Put it all together
We learned how to [display data](./displaying-data.html) in the previous chapter.
We've acquired a small arsenal of event binding techniques in this chapter.
Let's put it all together in a micro-app
that can display a list of heroes and add new heroes to that list.
figure.image-display
img(src='/resources/images/devguide/user-input/little-tour.png' alt="Little Tour of Heroes")
:markdown
Below is the entire "Little Tour of Heroes" micro-app in a single component.
We'll call out the highlights after we bask briefly in its minimalist glory.
<!--
This example in http://plnkr.co/edit/JWeIqq
-->
code-example(format="linenums" language="html" ).
import {bootstrap, Component CORE_DIRECTIVES} from 'angular2/core'
@Component({
selector: 'todo-list'
selector: 'little-tour',
template: `
&lt;ul&gt;
&lt;li *ngfor="#todo of todos"&gt;
{{ todo }}
&lt;/li&gt;
&lt;/ul&gt;
&lt;input #todotext (keyup)="doneTyping($event)"&gt;
&lt;button (click)="addTodo(todotext.value)"&gt;Add Todo&lt;/button&gt;
&lt;h4>Little Tour of Heroes&lt;/h4>
&lt;input #new-hero (keyup.enter)="addHero(newHero)">
&lt;button (click)=addHero(newHero)>Add&lt;/button>
&lt;ul>&lt;li *ng-for="#hero of heroes">{{hero}}&lt;/li>&lt;/ul>
&lt;div>There are so many heroes!&lt;/div>
`,
directives: [NgFor, NIf]
directives: [CORE_DIRECTIVES]
})
class TodoList {
todos: Array&lt;string&gt;;
class LittleTour {
heroes=['Windstorm', 'Bombasto', 'Magneta', 'Tornado'];
constructor() {
this.todos = ["Eat Breakfast", "Walk Dog", "Breathe"];
}
addTodo(todo: string) {
this.todos.push(todo);
}
doneTyping($event) {
if($event.which === 13) {
this.addTodo($event.target.value);
$event.target.value = null;
addHero(newHero) {
if (newHero.value) {
this.heroes.push(newHero.value);
newHero.value = null; // clear the newHero textbox
}
}
}
bootstrap(TodoList);
code-pane(language="javascript" name="ES5" format="linenums").
//ES5
function TodoList() {
this.todos = ["Eat Breakfast", "Walk Dog", "Breathe"];
bootstrap(LittleTour);
this.addTodo = function(todo) {
this.todos.push(todo);
};
:markdown
We've seen almost everything here before. A few things are new or bear repeating.
this.doneTyping = function($event) {
if($event.which === 13) {
this.addTodo($event.target.value);
$event.target.value = null;
}
}
}
### **Beware of camelCase variable names**
We enter new hero names in the `<input>` element so we chose `newHero` to be the name of the local template variable.
Unfortunately, we can't use that name when we declare the variable with (#).
The browser forces all attribute and element names to lowercase, turning what would be `#newHero`
into `#newhero`. We don't want a `newhero` variable name in our template expressions.
The Angular workaround is to spell the declaration in "snake case". When Angular encounters "#new-hero",it translates
that to `newHero` for template expressions ... which is exactly what we want.
### **keyup.enter - a KeyEvent filter**
We'll add a hero name when the user clicks the "Add" button or hits the enter key. We ignore all other keys.
If we bind to `(keyup)` our event handling expression hears every key event. We'd have to
examine every `$event.keyCode` and respond only if the value is "Enter".
Angular can filter the key events for us. Angular has a special syntax for keyboard events.
We can listen for just the "enter" key by binding to Angular's `keyup.enter` pseudo-event.
Then either the `keyup.enter` or the button click event
can invoke the component's `addHero` method.
### **newHero refers to the `<input>` element**
We can access the `newHero` variable from any sibling or child of the `<input>` element.
When the user clicks the button, we don't need a fancy css selector to
track down the textbox and extract its value.
The button simply passes the `newHero` textbox reference to its own click handling method.
That's a tremendous simplification, as anyone who's wrangled jQuery can confirm.
Ready access to the `<input>` element also makes it easy for the `addHero` method
to clear the textbox after processing the new hero.
### **The *ng-for repeater**
The `ng-for` directive repeats the template as many times as there are heroes in the `heroes` list.
We must remember to list `NgFor` among the directives used by the component's template
by importing the `CORE_DIRECTIVES` constant and adding it to the
@Component decorator's `directives` array.
We learned about `NgFor` in the "[Displaying Data](./displaying-data.html)" chapter.
.l-main-section
:markdown
## Next Steps
We've mastered the basic primitives for responding to user input and gestures.
As powerful as these primitives are, they are a bit clumsy for handling
large amounts of user input. We're operating down at the low level of events when
we should be writing two-way bindings between data entry fields and model properties.
Angular has a two-way binding called `NgModel` and we learn about it
in the `Forms` chapter.
TodoList.annotations = [
new angular.ComponentAnnotation({
selector: "todo-list"
}),
new angular.ViewAnnotation({
template:
'&lt;ul&gt;' +
'&lt;li *ng-for="#todo of todos">' +
'{{ todo }}' +
'&lt;/li&gt;' +
'&lt;/ul&gt;' +
'&lt;input #textbox (keyup)="doneTyping($event)">' +
'&lt;button (click)="addTodo(textbox.value)"&gt;Add Todo&lt;/button&gt;',
directives: [angular.NgFor, angular.NgIf]
})
];
document.addEventListener("DOMContentLoaded", function() {
angular.bootstrap(TodoList);
});

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