include _util-fns

// #docregion intro
:marked
  # Angular 2词汇表

  Angular 2 has a vocabulary of its own.
  Most Angular 2 terms are everyday English words
  with a specific meaning within the Angular system.

  Angular 2有自己的词汇表。
  虽然大多数的Angular 2短语都是日常用语，但是在Angular体系中，它们有特别的含义。

  We have gathered here the most prominent terms
  and a few less familiar ones that have unusual or
  unexpected definitions.

  我们搜集了最常用和少量不常用的词汇，它们具有独特或不符合直觉的含义。

  [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
  ## 注解（Annotation）
.l-sub-section
  :marked
    In practice a synonym for [Decoration](#decorator).
    
    [装饰器（Decoration）](#decorator)在实践中的同义词。
// #enddocregion a-1
// #docregion a-2
:marked
  ## Attribute Directive
  ## 属性型指令（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.

    [指令](#directive)分类中的一种。它允许监听或修改其它HTML元素、属性、组件的行为。它们通常用作HTML属性，就像它的名字所暗示的那样。
    
    The `ngClass` directive for adding and removing CSS class names is a good example of
    an Attribute Directive.
    
    `ngClass`指令就是典型的属性型指令。它可以添加或移除CSS类名。
// #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
  ## 封装桶（Barrel）
.l-sub-section
  :marked
    A **barrel** is an Angular library module consisting of a logical grouping of single-purpose modules
    such as `Component` and `Directive`.

    一个**封装桶**是一个模块库，包含了按照逻辑分组到一起的单一用途的多个模块，比如组件和指令。

    Familiar barrels include `angular2/core`, `angular2/common`, `angular2/platform/browser`,
    `angular2/http`, and `angular2/router`.

    你熟悉的封装桶包含`angular2/core`, `angular2/common`, `angular2/platform/browser`,
       `angular2/http`, 和 `angular2/router`.

    Barrels are packaged and shipped as [**bundles**](#bundle) that
    we may load with script tags in our `index.html`.

    封装桶被当做捆绑包[**bundles**](#bundle)打包和发布，以便我们通过Script标签在`index.html`页面里面装载。

    The script, `angular2.dev.js`, is a bundle.
    `angular2.dev.js`脚本就是一个捆绑包（bundle）

    Learn more in "[Modules, barrels and bundles](https://github.com/angular/angular/blob/master/modules/angular2/docs/bundles/overview.md)".
    获取更多关于模块，封装桶和捆绑包的信息："[Modules, barrels and bundles](https://github.com/angular/angular/blob/master/modules/angular2/docs/bundles/overview.md)"
:marked
  ## Binding
  ## 绑定
.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.

    几乎都是指的数据绑定[Data Binding](#data-binding)和将一个HTML对象属性绑定到一个数据对象属性的行为。

    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.

    有可能指的是依赖注入[Dependency Injection](#dependency-injection)在一个标志(Token)或钥匙(Key)和一个依赖提供商Dependency [provider](#provider)之间的绑定。
    这个用法很少，而且一般都应该在上下文中明确标示。

:marked
  ## Bootstrap
  ## 引导程序
.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).

    要启动一个Angular的应用程序，我们通过一个名叫`bootstrap`的函数方法来引导装入。这个`bootstrap`函数方法会识别应用程序的顶级“根”组件"root" [Component](#component)，
    并通过依赖注入系统[dependency injection system](#dependency-injection)选择性的注册服务提供商service [providers](#provider)。

    One can bootstrap multiple apps in the same `index.html`, each with its own top level root.
    你可以在同一个`index.html`启动多个程序，每个程序都有自己的顶级根组件。

:marked
  ## Bundle
  ## 捆绑包
.l-sub-section
  :marked
    Angular JavaScript libraries are shipped in **bundles** within an **npm package**
    such as [angular2](https://www.npmjs.com/package/angular2).

    Angular Javascript库是以一个**NPM包**（**npm package**），捆绑多个**捆绑包**（**bundles**）的形式发布的。
    比如[angular2](https://www.npmjs.com/package/angular2).

    The scripts `angular2.dev.js`, `http.js`, `router.js`, and `Rx.js` are
    familiar examples of bundles.

    `angular2.dev.js`, `http.js`, `router.js`, 和 `Rx.js`等脚本文件是比较常见的捆绑包（bundle）例子。


    A bundle contains one more more [**barrels**](#barrel)
    and each barrel contains a collection of logically related [modules](#module)

    一个捆绑包（bundle）包含了一个或多个**封装桶**[**barrels**](#barrel)

    Familiar barrels include `angular2/core`, `angular2/common`, `angular2/platform/browser`,
    `angular2/http`, `angular2/router`.

    常见的封装桶包括`angular2/core`, `angular2/common`, `angular2/platform/browser`,
        `angular2/http`, `angular2/router`等。

    Learn more in "[Modules, barrels and bundles](https://github.com/angular/angular/blob/master/modules/angular2/docs/bundles/overview.md)".
    获取更多关于模块，封装头和捆绑包的知识："[Modules, barrels and bundles](https://github.com/angular/angular/blob/master/modules/angular2/docs/bundles/overview.md)"。

<a id="C"></a>
.l-main-section
:marked
  ## camelCase
  ## 驼峰式命名法
.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_. 

    除了首字母外小写外，每一个单词或简写以大写字母开始的编写词汇或短语的方法叫做驼峰式命名法。

    Function, property, and method names are typically spelled in camelCase. Examples include: `square`, `firstName` and `getHeroes`.

    函数、属性和方法名字一般都是以驼峰式大小写的方式命名。比如`square`, `firstName` 和 `getHeroes`等。

    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*.

    这种形式也被叫做**小驼峰式命名法**（**lower camel case**），以便区分**大驼峰式命名法**（我们叫帕斯卡命名法）。
    当我们文档中使用“小驼峰式命名法” （“camelCase”）的时候，我们永远指的是小驼峰命名法。

:marked
  ## Component
  ## 组件
.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.

    组件是一个用来展示数据到视图[View](#view)，并处理几乎所有视图显示和用户互动逻辑的Angular类（Angular Class）。

    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).

    组件是Angular系统的最重要的基本单位之一。
    它其实是一个拥有模板[Template](#template)的指令[Directive](#directive)。

    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.

    开发人员在使用`#{atSym}Component` !{修饰器}!{decorator}来修饰一个组件类，就是把这个类附加到基本组件元数据（essential component metadata）上面。
    Angular需要利用这个基本组件元数的信息，来建立一个组件实例，把一个组件的模板作为视图画出来。

    Those familiar with "MVC" and "MVVM" patterns will recognize
    the Component in the role of "Controller" or "View Model".

    那些熟悉 "MVC" 和 "MVVM" 架构模式的应该能意识到组件充当了控制和视图模型的角色。
// #enddocregion b-c

// #docregion d1
<a id="D"></a>
.l-main-section
:marked
  ## dash-case
  ## 横杠分隔命名法
.l-sub-section
  :marked
    The practice of writing compound words or phrases such that each word is separated by a dash or hyphen (-). 

    使用横杠来分隔每个单词来编写词汇或短语的方法叫做横杠分隔命名法

    Directive selectors and the root of filenames are often spelled in dash-case. Examples include: `my-app` and the `hero-list.component.ts`.

    指令的选择器和文件名通常都是通过横杠分隔命名法来命名的。比如`my-app` and the `hero-list.component.ts`

    This form is also known as [kebab-case](#kebab-case).
    这种命名法也被叫做可芭比命名法[kebab-case](#kebab-case)

:marked
  ## Data Binding
  ## 数据绑定
.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](template-syntax.html#interpolation)
     * [Property Binding](template-syntax.html#property-binding)
     * [Event Binding](template-syntax.html#event-binding)
     * [Attribute Binding](template-syntax.html#attribute-binding)
     * [Class Binding](template-syntax.html#class-binding)
     * [Style Binding](template-syntax.html#style-binding)
     * [Two-way data binding with ngModel](template-syntax.html#ng-model)

    Learn more about data binding in the
    [Template Syntax](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](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 lastest 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](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](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](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 the `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](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/angular2/src/common/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 public-facing **library modules**
    called [**barrels**](#barrel). Barrels are groups of logically related modules.
    The `angular2/core` barrel is a good example.

    Learn more in "[Modules, barrels and bundles](https://github.com/angular/angular/blob/master/modules/angular2/docs/bundles/overview.md)".
// #enddocregion m2

// #docregion n-s
- 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](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](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](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](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.

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  ## Structural Directive
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    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

// #docregion t1
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  ## Template
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    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](template-syntax.html).

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  ## Template Expression
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    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](template-syntax.html#template-expressions) chapter.

// #enddocregion t1
// #docregion t2
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  ## Transpile
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    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
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    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
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  ## View
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    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).

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  ## Zone
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    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](#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