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include _util-fns
// #docregion intro
:marked
# Angular 2 Glossary
Angular 2 has a vocabulary of its own.
Most Angular 2 terms are everyday English words
with a specific meaning within the Angular system.
We have gathered here the most prominent terms
and a few less familiar ones that have unusual or
unexpected definitions.
[A](#A) [B](#B) [C](#C) [D](#D) [E](#E) [F](#F) [G](#G) [H](#H) [I](#I)
[J](#J) [K](#K) [L](#L) [M](#M) [N](#N) [O](#O) [P](#P) [Q](#Q) [R](#R)
[S](#S) [T](#T) [U](#U) [V](#V) [W](#W) [X](#X) [Y](#Y) [Z](#Z)
// #enddocregion intro
// #docregion a1
<a id="A"></a>
// #enddocregion a1
.l-main-section
:marked
## Annotation
.l-sub-section
:marked
In practice a synonym for [Decoration](#decorator).
// #enddocregion a-1
// #docregion a-2
:marked
## Attribute Directive
.l-sub-section
:marked
A category of [Directive](#directive) that can listen to and modify the behavior of
other HTML elements, attributes, properties, and components. They are usually represented
as HTML attributes, hence the name.
The `ngClass` directive for adding and removing CSS class names is a good example of
an Attribute Directive.
// #enddocregion a-2
// #docregion b-c
- var lang = current.path[1]
- var decorator = lang === 'dart' ? 'annotation' : '<a href="#decorator">decorator</a>'
- var atSym = lang === 'js' ? '' : '@'
<a id="B"></a>
.l-main-section
:marked
## Barrel
.l-sub-section
:marked
A barrel is a way to *rollup exports* from several modules into a single convenience module.
The barrel itself is a module file that re-exports *selected* exports of other modules.
Imagine three modules in a `heroes` folder:
code-example(format='').
// heroes/hero.component.ts
export class HeroComponent {}
// heroes/hero.model.ts
export class Hero {}
// heroes/hero.service.ts
export class HeroService {}
:marked
Without a barrel, a consumer would need three import statements:
code-example(format='').
import { HeroComponent } from '../heroes/hero.component.ts';
import { Hero } from '../heroes/hero.model.ts';
import { HeroService } from '../heroes/hero.service.ts';
:marked
We can add a barrel to the `heroes` folder (called `index` by convention) that exports all of these items:
code-example(format='').
export * from './hero.model.ts'; // re-export all of its exports
export * from './hero.service.ts'; // re-export all of its exports
export { HeroComponent } from './hero.component.ts'; // re-export the named thing
:marked
Now a consumer can import what it needs from the barrel.
code-example(format='').
import { Hero, HeroService } from '../heroes'; // index is implied
:marked
The Angular [scoped packages](#scoped-package) each have a barrel named `index`.
// #enddocregion b-c
:marked
That's why we can write this:
+makeExample('../docs/_fragments/quickstart/ts/app/app.component.ts', 'import')(format=".")
// #docregion b-c
:marked
## Binding
.l-sub-section
:marked
Almost always refers to [Data Binding](#data-binding) and the act of
binding an HTML object property to a data object property.
May refer to a [Dependency Injection](#dependency-injection) binding
between a "token" or "key" and a dependency [provider](#provider).
This more rare usage should be clear in context.
:marked
## Bootstrap
.l-sub-section
:marked
We launch an Angular application by "bootstrapping" it with the `bootstrap` method.
The `bootstrap` method identifies an application's top level "root" [Component](#component)
and optionally registers service [providers](#provider) with the
[dependency injection system](#dependency-injection).
One can bootstrap multiple apps in the same `index.html`, each with its own top level root.
<a id="C"></a>
.l-main-section
:marked
## camelCase
.l-sub-section
:marked
The practice of writing compound words or phrases such that each word or abbreviation begins with a capital letter
_except the first letter which is a lowercase letter_.
Function, property, and method names are typically spelled in camelCase. Examples include: `square`, `firstName` and `getHeroes`.
This form is also known as **lower camel case**, to distinguish it from **upper camel case** which we call [PascalCase](#pascalcase).
When we write "camelCase" in this documentation we always mean *lower camel case*.
:marked
## Component
.l-sub-section
:marked
An Angular class responsible for exposing data
to a [View](#view) and handling most of the view’s display
and user-interaction logic.
The Component is one of the most important building blocks in the Angular system.
It is, in fact, an Angular [Directive](#directive) with a companion [Template](#template).
The developer applies the `#{atSym}Component` !{decorator} to
the component class, thereby attaching to the class the essential component metadata
that Angular needs to create a component instance and render it with its template
as a view.
Those familiar with "MVC" and "MVVM" patterns will recognize
the Component in the role of "Controller" or "View Model".
// #enddocregion b-c
// #docregion d1
<a id="D"></a>
.l-main-section
:marked
## dash-case
.l-sub-section
:marked
The practice of writing compound words or phrases such that each word is separated by a dash or hyphen (`-`).
Directive selectors and the root of filenames are often spelled in dash-case. Examples include: `my-app` and `hero-list.component.ts`.
This form is also known as [kebab-case](#kebab-case).
:marked
## Data Binding
.l-sub-section
:marked
Applications display data values to a user and respond to user
actions (clicks, touches, keystrokes).
We could push application data values into HTML, attach
event listeners, pull changed values from the screen, and
update application data values ... all by hand.
Or we could declare the relationship between an HTML widget
and an application data source ... and let a data binding
framework handle the details.
Data Binding is that second approach. Angular has a rich
data binding framework with a variety of data binding
operations and supporting declaration syntax.
The many forms of binding include:
* [Interpolation](/docs/ts/latest/guide/template-syntax.html#interpolation)
* [Property Binding](/docs/ts/latest/guide/template-syntax.html#property-binding)
* [Event Binding](/docs/ts/latest/guide/template-syntax.html#event-binding)
* [Attribute Binding](/docs/ts/latest/guide/template-syntax.html#attribute-binding)
* [Class Binding](/docs/ts/latest/guide/template-syntax.html#class-binding)
* [Style Binding](/docs/ts/latest/guide/template-syntax.html#style-binding)
* [Two-way data binding with ngModel](/docs/ts/latest/guide/template-syntax.html#ng-model)
Learn more about data binding in the
[Template Syntax](/docs/ts/latest/guide/template-syntax.html#data-binding) chapter.
// #enddocregion d1
<a id="decorator"></a> <a id="decoration"></a>
:marked
## Decorator | Decoration
.l-sub-section
:marked
A Decorator is a **function** that adds metadata to a class, its members (properties, methods) and function arguments.
Decorators are a JavaScript language [feature](https://github.com/wycats/javascript-decorators), implemented in TypeScript and proposed for ES2016 (AKA ES7).
We apply a decorator by positioning it
immediately above or to the left of the thing it decorates.
Angular has its own set of decorators to help it interoperate with our application parts.
Here is an example of a `@Component` decorator that identifies a
class as an Angular [Component](#component) and an `@Input` decorator applied to a property
of that component.
The elided object argument to the `@Component` decorator would contain the pertinent component metadata.
```
@Component({...})
export class AppComponent {
constructor(@Inject('SpecialFoo') public foo:Foo) {}
@Input() name:string;
}
```
The scope of a decorator is limited to the language feature
that it decorates. None of the decorations shown here will "leak" to other
classes appearing below it in the file.
.alert.is-important
:marked
Always include the parentheses `()` when applying a decorator.
A decorator is a **function** that must be called when applied.
// #docregion d2
:marked
## Dependency Injection
.l-sub-section
:marked
Dependency Injection is both a design pattern and a mechanism
for creating and delivering parts of an application to other
parts of an application that request them.
Angular developers prefer to build applications by defining many simple parts
that each do one thing well and then wire them together at runtime.
These parts often rely on other parts. An Angular [Component](#component)
part might rely on a service part to get data or perform a calculation. When a
part "A" relies on another part "B", we say that "A" depends on "B" and
that "B" is a dependency of "A".
We can ask a "Dependency Injection System" to create "A"
for us and handle all the dependencies.
If "A" needs "B" and "B" needs "C", the system resolves that chain of dependencies
and returns a fully prepared instance of "A".
Angular provides and relies upon its own sophisticated
[Dependency Injection](dependency-injection.html) system
to assemble and run applications by "injecting" application parts
into other application parts where and when needed.
At the core is an [`Injector`](#injector) that returns dependency values on request.
The expression `injector.get(token)` returns the value associated with the given token.
A token is an Angular type (`OpaqueToken`). We rarely deal with tokens directly; most
methods accept a class name (`Foo`) or a string ("foo") and Angular converts it
to a token. When we write `injector.get(Foo)`, the injector returns
the value associated with the token for the `Foo` class, typically an instance of `Foo` itself.
Angular makes similar requests internally during many of its operations
as when it creates a [`Component`](#AppComponent) for display.
The `Injector` maintains an internal map of tokens to dependency values.
If the `Injector` can't find a value for a given token, it creates
a new value using a `Provider` for that token.
A [Provider](#provider) is a recipe for
creating new instances of a dependency value associated with a particular token.
An injector can only create a value for a given token if it has
a `Provider` for that token in its internal provider registry.
Registering providers is a critical preparatory step.
Angular registers some of its own providers with every injector.
We can register our own providers. Quite often the best time to register a `Provider`
is when we [bootstrap](#bootstrap) the application.
There are other opportunities to register as well.
Learn more in the [Dependency Injection](/docs/ts/latest/guide/dependency-injection.html) chapter.
:marked
## Directive
.l-sub-section
:marked
An Angular class responsible for creating, re-shaping, and interacting with HTML elements
in the browser DOM. Directives are Angular's most fundamental feature.
A Directive is almost always associated with an HTML element or attribute.
We often refer to such an element or attribute as the directive itself.
When Angular finds a directive in an HTML template,
it creates the matching directive class instance
and gives that instance control over that portion of the browser DOM.
Developers can invent custom HTML markup (e.g., `<my-directive>`) to
associate with their custom directives. They add this custom markup to HTML templates
as if they were writing native HTML. In this way, directives become extensions of
HTML itself.
Directives fall into one of three categories:
1. [Components](#component) that combine application logic with an HTML template to
render application [views]. Components are usually represented as HTML elements.
They are the building blocks of an Angular application and the
developer can expect to write a lot of them.
1. [Attribute Directives](#attribute-directive) that can listen to and modify the behavior of
other HTML elements, attributes, properties, and components. They are usually represented
as HTML attributes, hence the name.
1. [Structural Directives](#structural-directive), a directive responsible for
shaping or re-shaping HTML layout, typically by adding, removing, or manipulating
elements and their children.
// #enddocregion d2
// #docregion e1
<a id="E"></a>
// #enddocregion e1
// #docregion e2
.l-main-section
:marked
## ECMAScript
.l-sub-section
:marked
The [official JavaScript language specification](https://en.wikipedia.org/wiki/ECMAScript).
The latest approved version of JavaScript is
[ECMAScript 2015](http://www.ecma-international.org/ecma-262/6.0/)
(AKA "ES2015" or "ES6") and many Angular 2 developers will write their applications
either in this version of the language or a dialect that strives to be
compatible with it such as [TypeScript](#typesScript).
Most modern browsers today only support the prior "ECMAScript 5" (AKA ES5) standard.
Applications written in ES2015 or one of its dialects must be "[transpiled](#transpile)"
to ES5 JavaScript.
Angular 2 developers may choose to write in ES5 directly.
:marked
## ECMAScript 2015
.l-sub-section
:marked
The latest released version of JavaScript,
[ECMAScript 2015](http://www.ecma-international.org/ecma-262/6.0/)
(AKA "ES2015" or "ES6")
:marked
## ES2015
.l-sub-section
:marked
Short hand for "[ECMAScript 2015](#ecmascript=2015)".
:marked
## ES6
.l-sub-section
:marked
Short hand for "[ECMAScript 2015](#ecmascript=2015)".
:marked
## ES5
.l-sub-section
:marked
Short hand for "ECMAScript 5", the version of JavaScript run by most modern browsers.
See [ECMAScript](#ecmascript).
// #enddocregion e2
// #docregion f-l
<a id="F"></a>
<a id="G"></a>
<a id="H"></a>
<a id="I"></a>
.l-main-section
:marked
## Injector
.l-sub-section
:marked
An object in the Angular [dependency injection system](#dependency-injection)
that can find a named "dependency" in its cache or create such a thing
with a registered [provider](#provider).
:marked
## Input
.l-sub-section
:marked
A directive property that can be the ***target*** of a
[Property Binding](/docs/ts/latest/guide/template-syntax.html#property-binding).
Data values flow *into* this property from the data source identified
in the template expression to the right of the equal sign.
See the [Template Syntax](/docs/ts/latest/guide/template-syntax.html#inputs-outputs) chapter.
:marked
## Interpolation
.l-sub-section
:marked
A form of [Property Data Binding](#data-binding) in which a
[template expression](#template-expression) between double-curly braces
renders as text. That text may be concatenated with neighboring text
before it is assigned to an element property
or displayed between element tags as in this example.
code-example(language="html" escape="html").
<label>My current hero is {{hero.name}}</label>
:marked
Learn more about interpolation in the
[Template Syntax](/docs/ts/latest/guide/template-syntax.html#interpolation) chapter.
<a id="J"></a>
.l-main-section
<a id="K"></a>
:marked
## kebab-case
.l-sub-section
:marked
The practice of writing compound words or phrases such that each word is separated by a dash or hyphen (`-`).
Directive selectors and the root of filenames are often spelled in kebab-case. Examples include: `my-app` and `hero-list.component.ts`.
This form is also known as [dash-case](#dash-case).
<a id="L"></a>
.l-main-section
:marked
## Lifecycle Hooks
.l-sub-section
:marked
[Directives](#directive) and [Components](#component) have a lifecycle
managed by Angular as it creates, updates and destroys them.
Developers can tap into key moments in that lifecycle by implementing
one or more of the "Lifecycle Hook" interfaces.
Each interface has a single hook method whose name is the interface name prefixed with `ng`.
For example, the `OnInit` interface has a hook method names `ngOnInit`.
Angular calls these hook methods in the following order:
* `ngOnChanges` - called when an [input](#input)/[output](#output) binding values change
* `ngOnInit` - after the first `ngOnChanges`
* `ngDoCheck` - developer's custom change detection
* `ngAfterContentInit` - after component content initialized
* `ngAfterContentChecked` - after every check of component content
* `ngAfterViewInit` - after component's view(s) are initialized
* `ngAfterViewChecked` - after every check of a component's view(s)
* `ngOnDestroy` - just before the directive is destroyed.
Learn more in the [Lifecycle Hooks](/docs/ts/latest/guide/lifecycle-hooks.html) chapter.
// #enddocregion f-l
// #docregion m1
<a id="M"></a>
// #enddocregion m1
// #docregion m2
.l-main-section
:marked
## Module
.l-sub-section
:marked
Angular apps are modular.
In general, we assemble our application from many modules, both the ones we write ourselves
and the ones we acquire from others.
A typical module is a cohesive block of code dedicated to a single purpose.
A module **exports** something of value in that code, typically one thing such as a class.
A module that needs that thing, **imports** it.
The structure of Angular modules and the import/export syntax
is based on the [ES2015](#es2015) module standard
described [here](http://www.2ality.com/2014/09/es6-modules-final.html).
An application that adheres to this standard requires a module loader to
load modules on request and resolve inter-module dependencies.
Angular does not ship with a module loader and does not have a preference
for any particular 3rd party library (although most samples use SystemJS).
Application developers may pick any module library that conforms to the standard
Modules are typically named after the file in which the exported thing is defined.
The Angular [DatePipe](https://github.com/angular/angular/blob/master/modules/@angular/common/src/pipes/date_pipe.ts)
class belongs to a feature module named `date_pipe` in the file `date_pipe.ts`.
Developers rarely access Angular feature modules directly.
We usually import them from one of the Angular [scoped packages](#scoped-package) such as `@angular/core`.
// #enddocregion m2
// #docregion n-s-1
- var lang = current.path[1]
- var decorator = lang === 'dart' ? 'annotation' : '<a href="#decorator">decorator</a>'
- var atSym = lang === 'js' ? '' : '@'
<a id="N"></a>
<a id="O"></a>
.l-main-section
:marked
## Output
.l-sub-section
:marked
A directive property that can be the ***target*** of an
[Event Binding](/docs/ts/latest/guide/template-syntax.html#property-binding).
Events stream *out* of this property to the receiver identified
in the template expression to the right of the equal sign.
See the [Template Syntax](/docs/ts/latest/guide/template-syntax.html#inputs-outputs) chapter.
.l-main-section
<a id="P"></a>
:marked
## PascalCase
.l-sub-section
:marked
The practice of writing compound words or phrases such that each word or abbreviation begins with a capital letter.
Class names are typically spelled in PascalCase. Examples include: `Person` and `Customer`.
This form is also known as **upper camel case**, to distinguish it from **lower camel case** which we simply call [camelCase](#camelcase).
In this documentation, "PascalCase" means *upper camel case* and "camelCase" means *lower camel case*.
:marked
## Pipe
.l-sub-section
:marked
An Angular pipe is a function that transforms input values to output values for
display in a [view](#view). We use the `#{atSym}Pipe` !{decorator}
to associate the pipe function with a name. We then can use that
name in our HTML to declaratively transform values on screen.
Here's an example that uses the built-in `currency` pipe to display
a numeric value in the local currency.
code-example(language="html" escape="html").
<label>Price: </label>{{product.price | currency}}
:marked
Learn more in the chapter on [pipes](/docs/ts/latest/guide/pipes.html) .
:marked
## Provider
.l-sub-section
:marked
A Provider creates a new instance of a dependency for the Dependency Injection system.
It relates a lookup token to code - sometimes called a "recipe" - that can create a dependency value.
For example, `new Provider(Foo, {useClass: Foo})` creates a `Provider`
that relates the `Foo` token to a function that creates a new instance of the `Foo` class.
There are other ways to create tokens and recipes.
See [Dependency Injection](#dependency-injection) chapter to learn more.
.l-main-section
<a id="Q"></a>
<a id="R"></a>
:marked
## Router
.l-sub-section
:marked
Most applications consist of many screens or [views](#view).
The user navigates among them by clicking links and buttons
and taking other similar actions that cause the application to
replace one view with another.
The Angular [Component Router](/docs/ts/latest/guide/router.html) is a richly featured mechanism for configuring
and managing the entire view navigation process including the creation and destruction
of views.
:marked
## Routing Component
.l-sub-section
:marked
A [Component](#component) with an attached router.
In most cases, the component became attached to a [router](#router) by means
of a `#{atSym}RouterConfig` #{decorator} that defined routes to views controlled by this component.
The component's template has a `RouterOutlet` element where it can display views produced by the router.
It likely has anchor tags or buttons with `RouterLink` directives that users can click to navigate.
<a id="S"></a>
.l-main-section
// #enddocregion n-s-1
:marked
## Scoped Package
.l-sub-section
:marked
Angular modules are delivered within *scoped packages* such as `@angular/core`, `@angular/common`, `@angular/platform-browser-dynamic`,
`@angular/http`, and `@angular/router`.
A [*scoped package*](https://docs.npmjs.com/misc/scope) is a way to group related *npm* packages.
We import a scoped package the same way we'd import a *normal* package.
The only difference, from a consumer perspective,
is that the package name begins with the Angular *scope name*, `@angular`.
+makeExample('../docs/_fragments/architecture/ts/app/app.component.ts', 'import')(format=".")
// #docregion n-s-2
:marked
## Structural Directive
.l-sub-section
:marked
A category of [Directive](#directive) that can
shape or re-shape HTML layout, typically by adding, removing, or manipulating
elements and their children.
The `ngIf` "conditional element" directive and the `ngFor` "repeater" directive are
good examples in this category.
// #enddocregion n-s-2
// #docregion t1
<a id="T"></a>
.l-main-section
:marked
## Template
.l-sub-section
:marked
A template is a chunk of HTML that Angular uses to render a [view](#view) with
the support and continuing guidance of an Angular [Directive](#directive),
most notably a [Component](#component).
We write templates in a special [Template Syntax](/docs/ts/latest/guide/template-syntax.html).
:marked
## Template Expression
.l-sub-section
:marked
An expression in a JavaScript-like syntax that Angular evaluates within
a [data binding](#data-binding). Learn how to write template expressions
in the [Template Syntax](/docs/ts/latest/guide/template-syntax.html#template-expressions) chapter.
// #enddocregion t1
// #docregion t2
:marked
## Transpile
.l-sub-section
:marked
The process of transforming code written in one form of JavaScript
(e.g., TypeScript) into another form of JavaScript (e.g., [ES5](#es5)).
:marked
## TypeScript
.l-sub-section
:marked
A version of JavaScript that supports most [ECMAScript 2015](#ecmascript=2015)
language features and many features that may arrive in future versions
of JavaScript such as [Decorators](#decorator).
TypeScript is also noteable for its optional typing system which gives
us compile-time type-checking and strong tooling support (e.g. "intellisense",
code completion, refactoring, and intelligent search). Many code editors
and IDEs support TypeScript either natively or with plugins.
TypeScript is the preferred language for Angular 2 development although
we are welcome to write in other JavaScript dialects such as [ES5](#es5).
Angular 2 itself is written in TypeScript.
Learn more about TypeScript on its [website](http://www.typescriptlang.org/).
// #enddocregion t2
// #docregion u-z
<a id="U"></a>
<a id="V"></a>
.l-main-section
:marked
## View
.l-sub-section
:marked
A view is a portion of the screen that displays information and responds
to user actions such as clicks, mouse moves, and keystrokes.
Angular renders a view under the control of one or more [Directives](#directive),
especially [Component](#component) directives and their companion [Templates](#template).
The Component plays such a prominent role that we often
find it convenient to refer to a component as a view.
Views often contain other views and any view might be loaded and unloaded
dynamically as the user navigates through the application, typically
under the control of a [router](#router).
.l-main-section
<a id="W"></a>
<a id="X"></a>
<a id="Y"></a>
<a id="Z"></a>
:marked
## Zone
.l-sub-section
:marked
Zones are a mechanism for encapsulating and intercepting
a JavaScript application's asynchronous activity.
The browser DOM and JavaScript have a limited number
of asynchronous activities, activities such as DOM events (e.g., clicks),
[promises](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise), and
[XHR](https://developer.mozilla.org/en-US/docs/Web/API/XMLHttpRequest)
calls to remote servers.
Zones intercept all of these activities and give a "zone client" the opportunity
to take action before and after the async activity completes.
Angular runs our application in a zone where it can respond to
asynchronous events by checking for data changes and updating
the information it displays via [data binding](#data-binding).
Learn more about zones in this
[Brian Ford video](https://www.youtube.com/watch?v=3IqtmUscE_U).
// #enddocregion u-z
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