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@ -1,8 +1,8 @@
# Angular Glossary
Angular has its own vocabulary.
Most Angular terms are common English words
with a specific meaning within the Angular system.
Most Angular terms are common English words or computing terms
that have a specific meaning within the Angular system.
This glossary lists the most prominent terms
and a few less familiar ones that have unusual or
@ -19,14 +19,19 @@ unexpected definitions.
## Ahead-of-time (AOT) compilation
You can compile Angular applications at build time.
By compiling your application using the compiler-cli, `ngc`, you can bootstrap directly to a module factory, meaning you don't need to include the Angular compiler in your JavaScript bundle.
Ahead-of-time compiled applications also benefit from decreased load time and increased performance.
The Angular ahead-of-time (AOT) compiler converts your Angular HTML and TypeScript code
into efficient JavaScript code during the build phase before the browser downloads
and runs that code.
This is the best compilation mode for production environments, with decreased load time and increased performance.
By compiling your application using the `ngc` command-line tool, you can bootstrap directly to a module factory, meaning you don't need to include the Angular compiler in your JavaScript bundle.
Compare [just-in-time (JIT) compilation](guide/glossary#jit).
## Annotation
In practice, a synonym for [Decoration](guide/glossary#decorator).
A structure that provides metadata for a class. See [Decorator](guide/glossary#decorator).
{@a attribute-directive}
@ -41,107 +46,72 @@ A category of [directive](guide/glossary#directive) that can listen to and modif
other HTML elements, attributes, properties, and components. They are usually represented
as HTML attributes, hence the name.
For example, you can use the `ngClass` directive to add and remove CSS class names.
Learn about them in the [_Attribute Directives_](guide/attribute-directives) guide.
Learn more in the [_Attribute Directives_](guide/attribute-directives) guide.
{@a B}
## Barrel
A way to *roll up exports* from several ES2015 modules into a single convenient ES2015 module.
The barrel itself is an ES2015 module file that re-exports selected exports of other ES2015 modules.
For example, imagine three ES2015 modules in a `heroes` folder:
<code-example>
// heroes/hero.component.ts
export class HeroComponent {}
// heroes/hero.model.ts
export class Hero {}
// heroes/hero.service.ts
export class HeroService {}
</code-example>
Without a barrel, a consumer needs three import statements:
<code-example>
import { HeroComponent } from '../heroes/hero.component.ts';
import { Hero } from '../heroes/hero.model.ts';
import { HeroService } from '../heroes/hero.service.ts';
</code-example>
You can add a barrel to the `heroes` folder (called `index`, by convention) that exports all of these items:
<code-example>
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
</code-example>
Now a consumer can import what it needs from the barrel.
<code-example>
import { Hero, HeroService } from '../heroes'; // index is implied
</code-example>
The Angular [scoped packages](guide/glossary#scoped-package) each have a barrel named `index`.
<div class="alert is-important">
You can often achieve the same result using [NgModules](guide/glossary#ngmodule) instead.
</div>
## Binding
Usually refers to [data binding](guide/glossary#data-binding) and the act of
binding an HTML object property to a data object property.
Generally, the practice of setting a variable or property to a data value.
Within Angular, typically refers to [data binding](guide/glossary#data-binding),
which coordinates DOM object properties with data object properties.
Sometimes refers to a [dependency-injection](guide/glossary#dependency-injection) binding
between a "token"&mdash;also referred to as a "key"&mdash;and a dependency [provider](guide/glossary#provider).
between a [token](guide/glossary#token) and a dependency [provider](guide/glossary#provider).
## Bootstrap
You launch an Angular application by "bootstrapping" it using the application root NgModule (`AppModule`).
A way to initialize and launch an app or system.
Bootstrapping identifies an application's top level "root" [component](guide/glossary#component),
which is the first component that is loaded for the application.
You can bootstrap multiple apps in the same `index.html`, each app with its own top-level root.
In Angular, an app's root NgModule (`AppModule`) has a `bootstrap` property that identifies the app's top-level [components](guide/glossary#component).
During the bootstrap process, Angular creates and inserts these components into the `index.html` host web page.
You can bootstrap multiple apps in the same `index.html`, each app with its own components.
Learn more in the [_Bootstrapping_](guide/bootstrapping) guide.
{@a C}
{@a case-conventions}
{@a dash-case}
{@a camelcase}
{@a kebab-case}
## Case conventions
Angular uses capitalization conventions to distinguish the names of various types, as described in the [Style Guide "Naming" section](guide/styleguide#02-01).
- camelCase : symbols, properties, methods, pipe names, interfaces, non-component directive selectors, constants
- UpperCamelCase (also called PascalCase): Class names
- dash-case (also called "kebab-case"): descriptive part of file names, component selectors
- camelCase : symbols, properties, methods, pipe names, non-component directive selectors, constants
- UpperCamelCase (or PascalCase): Class names, including classes that define components, interfaces, NgModules, directives, pipes, and so on.
- dash-case (or "kebab-case"): descriptive part of file names, component selectors
- underscore_case (or "snake_case"): not typically used in Angular
- UPPER_SNAKE_CASE : traditional for constants (acceptable, but prefer camelCase)
- UPPER_UNDERSCORE_CASE (or UPPER_SNAKE_CASE): traditional for constants (acceptable, but prefer camelCase)
{@a class-decorator}
## Class decorator
A [decorator](guide/glossary#decorator) statement immediately before a class definition that declares the class to be of the given type, and provides metadata suitable to the type.
The following class types can be declared:
- `@Component`
- `@Directive`
- `@Pipe`
- `@Injectable`
- `@NgModule`
{@a class-field-decorator}
## Class field decorator
A [decorator](guide/glossary#decorator) statement immediately before a field in a class definition that declares the type of that field. Some examples are `@Input` and `@Output`.
## CLI
The Angular CLI is a `command line interface` tool that can create a project, add files, and perform a variety of ongoing development tasks such as testing, bundling, and deployment.
The [Angular CLI](https://cli.angular.io/) is a command-line tool that can create a project, add files, and perform a variety of ongoing development tasks such as testing, bundling, and deployment.
Learn more in the [Getting Started](guide/quickstart) guide.
@ -149,18 +119,13 @@ Learn more in the [Getting Started](guide/quickstart) guide.
## Component
An Angular class responsible for exposing data to a [view](guide/glossary#view) and handling most of the view’s display and user-interaction logic.
A class with the `@Component` [decorator](guide/glossary#decorator) that associates it with a companion [template](guide/glossary#template).
The *component* is one of the most important building blocks in the Angular system.
It is, in fact, an Angular [directive](guide/glossary#directive) with a companion [template](guide/glossary#template).
A component is a special type of [directive](guide/glossary#directive) that represents a [view](guide/glossary#view).The `@Component` decorator extends the `@Directive` decorator with template-oriented features.
Apply the `@Component` [decorator](guide/glossary#decorator) to
the component class, thereby attaching to the class the essential component metadata
that Angular needs to create a component instance and render the component with its template
as a view.
An Angular component class is responsible for exposing data and handling most of the view's display and user-interaction logic through [data binding](guide/glossary#data-binding).
Those familiar with "MVC" and "MVVM" patterns will recognize
the component in the role of "controller" or "view model".
Read more about components, templates, and views in the [Architecture](guide/architecture) guide.
{@a custom-element}
@ -189,10 +154,7 @@ Data binding is an alternative to manually pushing application data values into
event listeners, pulling changed values from the screen, and
updating application data values.
Angular has a rich data-binding framework with a variety of data-binding
operations and supporting declaration syntax.
Read about the following forms of binding in the [Template Syntax](guide/template-syntax) page:
Read about the following forms of binding in the [Template Syntax](guide/template-syntax) page:
* [Interpolation](guide/template-syntax#interpolation).
* [Property binding](guide/template-syntax#property-binding).
@ -202,99 +164,54 @@ operations and supporting declaration syntax.
* [Style binding](guide/template-syntax#style-binding).
* [Two-way data binding with ngModel](guide/template-syntax#ngModel).
{@a declarable}
## Declarable
A class type that you can add to the `declarations` list of an [NgModule](guide/glossary#ngmodule).
You can declare [components](guide/glossary#component), [directives](guide/glossary#directive), and [pipes](guide/glossary#pipe).
Do not declare the following:
- A class that's already declared in another NgModule.
- An array of directives imported from another package. For example, don't declare `FORMS_DIRECTIVES` from `@angular/forms`.
- NgModule classes.
- Service classes.
- Non-Angular classes and objects, such as strings, numbers, functions, entity models, configurations, business logic, and helper classes
{@a decorator}
{@a decoration}
## Decorator | decoration
A *function* that adds metadata to a class, its members (properties, methods) and function arguments.
Decorators (also called annotations) are an experimental (stage 2), JavaScript language [feature](https://github.com/wycats/javascript-decorators). TypeScript adds support for decorators.
A function that modifies the immediately following class or property definition.
Decorators (also called annotations) are an experimental (stage 2), JavaScript language [feature](https://github.com/wycats/javascript-decorators).
TypeScript adds support for decorators.
To apply a decorator, position it immediately above or to the left of the item it decorates.
Angular defines decorators that attach metadata to classes or properties so that it knows what those classes or properties mean and how they should work.
Angular has its own set of decorators to help it interoperate with your application parts.
The following example is a `@Component` decorator that identifies a
class as an Angular [component](guide/glossary#component) and an `@Input` decorator applied to the `name` property
of that component. The elided object argument to the `@Component` decorator would contain the pertinent component metadata.
See [Class decorator](guide/glossary#class-decorator), [Class field decorator](guide/glossary#class-field-decorator).
```
@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 that follow it in the file.
<div class="alert is-important">
Always include parentheses `()` when applying a decorator.
</div>
{@a di}
## Dependency injection
A design pattern and mechanism
for creating and delivering parts of an application to other
parts of an application that request them.
A design pattern and mechanism for creating and delivering parts of an application (dependencies) to other parts of an application that require them.
Angular developers prefer to build applications by defining many simple parts
that each do one thing well and then wiring them together at runtime.
In Angular, dependencies are typically services, but can also be values, such as strings or functions. An [injector](guide/glossary#injector) for an app (created automatically during bootstrap) creates dependencies when needed, using a registered [provider](guide/glossary#provider) of the service or value. Different providers can provide different implementations of the same service.
These parts often rely on other parts. An Angular [component](guide/glossary#component)
part might rely on a service part to get data or perform a calculation. When
part "A" relies on another part "B," you say that "A" depends on "B" and
that "B" is a dependency of "A."
Learn more in the [Dependency Injection](guide/dependency-injection) guide.
You 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."
{@a di-token}
## DI token
Angular provides and relies upon its own sophisticated
dependency-injection system
to assemble and run applications by "injecting" application parts
into other application parts where and when needed.
At the core, an [`injector`](guide/glossary#injector) returns dependency values on request.
The expression `injector.get(token)` returns the value associated with the given token.
A token is an Angular type (`InjectionToken`). You rarely need to work with tokens directly; most
methods accept a class name (`Foo`) or a string ("foo") and Angular converts it
to a token. When you write `injector.get(Foo)`, the injector returns
the value associated with the token for the `Foo` class, typically an instance of `Foo` itself.
During many of its operations, Angular makes similar requests internally, such as when it creates a [`component`](guide/glossary#component) 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](guide/glossary#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.
You can register your own providers.
Read more in the [Dependency Injection](guide/dependency-injection) page.
A lookup token associated with a dependency [provider](guide/glossary#provider), for use with the [dependency injection](guide/glossary#di) system.
{@a directive}
@ -305,34 +222,25 @@ Read more in the [Dependency Injection](guide/dependency-injection) page.
## Directive
An Angular class responsible for creating, reshaping, and interacting with HTML elements
in the browser DOM. The directive is Angular's most fundamental feature.
A class with the `@Directive` [decorator](guide/glossary#decorator) that can modify the structure of the DOM, or modify attributes in the DOM and component data model.
A directive is usually associated with an HTML element or attribute.
This element or attribute is often referred to as the directive itself.
A directive class is usually associated with an HTML element or attribute, and that element or attribute is often referred to as the directive itself.
When Angular finds a directive in an HTML [template](guide/glossary#template), it creates the matching directive class instance and gives the instance control over that portion of the browser DOM.
When Angular finds a directive in an HTML template,
it creates the matching directive class instance
and gives the instance control over that portion of the browser DOM.
There are three categories of directive:
- [Components](guide/glossary#component) use `@Component` (an extension of `@Directive`) to associate a template with a class.
- [Attribute directives](guide/glossary#attribute-directive) modify behavior and appearance of page elements.
- [Structural directives](guide/glossary#structural-directive) modify the structure of the DOM.
You can invent custom HTML markup (for example, `<my-directive>`) to
associate with your custom directives. You add this custom markup to HTML templates
as if you were writing native HTML. In this way, directives become extensions of
HTML itself.
Angular supplies a number of built-in directives that begin with the `ng` prefix. You can also create new directives to implement your own functionality.
You associate a _selector_ (an HTML tag such as `<my-directive>`) with a custom directive, thereby extending the [template syntax](guide/template-syntax) that you can use in your apps.
Directives fall into one of the following categories:
* [Components](guide/glossary#component) combine application logic with an HTML template to
render application [views](guide/glossary#view). Components are usually represented as HTML elements.
They are the building blocks of an Angular application.
## Domain-specific language (DSL)
* [Attribute directives](guide/glossary#attribute-directive) 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.
A special-purpose library or API; see [Domain-specific language](https://en.wikipedia.org/wiki/Domain-specific_language).
* [Structural directives](guide/glossary#structural-directive) are responsible for
shaping or reshaping HTML layout, typically by adding, removing, or manipulating
elements and their children.
Angular extends TypeScript with domain-specific languages for a number of domains relevant to Angular apps, defined in ngModules such as [animations](guide/animations), [forms](guide/forms), and [routing and navigation](guide/router).
{@a dynamic-components}
@ -350,7 +258,9 @@ See also [Custom element](guide/glossary#custom-element), which provides an easi
The [official JavaScript language specification](https://en.wikipedia.org/wiki/ECMAScript).
Not all browsers support the latest ECMAScript standard, but you can use transpilers (like [TypeScript](guide/glossary#typescript)) to write code using the latest features, which will then be transpiled to code that runs on versions that are supported by browsers.
Not all browsers support the latest ECMAScript standard, but you can use a [transpiler](guide/glossary#transpile) (like [TypeScript](guide/glossary#typescript)) to write code using the latest features, which will then be transpiled to code that runs on versions that are supported by browsers.
To learn more, see the [Browser Support](guide/browser-support) page.
{@a element}
@ -363,6 +273,13 @@ The documentation generally refers to either elements (`ElementRef` instances) o
Compare [Custom element](guide/glossary#custom-element).
## Entry point
A JavaScript ID that makes parts of an NPM package available for import by other code.
The Angular [scoped packages](guide/glossary#scoped-package) each have an entry point named `index`.
Within Angular, use [NgModules](guide/glossary#ngmodule) to achieve the same result.
{@a F}
@ -374,6 +291,16 @@ Compare [Custom element](guide/glossary#custom-element).
{@a I}
{@a injectable}
## Injectable
An Angular class or other definition that provides a dependency using the [dependency injection](guide/glossary#di) mechanism. An injectable class is marked by the `@Injectable` [decorator](guide/glossary#decorator).
Both a [service](guide/glossary#service) and a [component](guide/glossary#component) that depends on that service must be marked as injectable. Other items, such as constant values, can be injectable.
{@a injector}
## Injector
An object in the Angular [dependency-injection system](guide/glossary#dependency-injection)
@ -383,19 +310,19 @@ with a registered [provider](guide/glossary#provider). Injectors are created for
## Input
A directive property that can be the *target* of a
[property binding](guide/template-syntax#property-binding) (explained in detail in the [Template Syntax](guide/template-syntax) page).
Data values flow *into* this property from the data source identified
in the template expression to the right of the equal sign.
When defining a [directive](guide/glossary#directive), the `@Input` decorator on a directive property makes that property available as a *target* of a
[property binding](guide/template-syntax#property-binding).
Data values flow into an input property from the data source identified
in the [template expression](guide/glossary#template-expression) to the right of the equal sign.
See the [Input and output properties](guide/template-syntax#inputs-outputs) section of the [Template Syntax](guide/template-syntax) page.
To learn more, see [input and output properties](guide/template-syntax#inputs-outputs).
## Interpolation
A form of [property data binding](guide/glossary#data-binding) in which a
[template expression](guide/glossary#template-expression) between double-curly braces
renders as text. That text may be concatenated with neighboring text
renders as text. That text can be concatenated with neighboring text
before it is assigned to an element property
or displayed between element tags, as in this example.
@ -422,9 +349,10 @@ See [ECMAScript](guide/glossary#ecma), [TypeScript](guide/glossary#typescript).
## Just-in-time (JIT) compilation
A bootstrapping method of compiling components and modules in the browser
and launching the application dynamically. Just-in-time mode is a good choice during development.
Consider using the [ahead-of-time](guide/glossary#aot) mode for production apps.
The Angular Just-in-Time (JIT) compiler converts your Angular HTML and TypeScript code into efficient JavaScript code at run time, as part of bootstrapping.
JIT compilation is the default when you run Angular's `ng build` and `ng serve` CLI commands, and is a good choice during development. JIT mode is strongly discouraged for production use because it results in large application payloads that hinder the bootstrap performance.
Compare [ahead-of-time (AOT) compilation](guide/glossary#aot).
{@a K}
@ -432,13 +360,17 @@ Consider using the [ahead-of-time](guide/glossary#aot) mode for production apps.
{@a L}
## Lifecycle hooks
{@a lazy-load}
[Directives](guide/glossary#directive) and [components](guide/glossary#component) have a lifecycle
managed by Angular as it creates, updates, and destroys them.
## Lazy loading
You can tap into key moments in that lifecycle by implementing
one or more of the lifecycle hook interfaces.
Lazy loading speeds up application load time by splitting the application into multiple bundles and loading them on demand.
For example, dependencies can be lazy-loaded as needed&emdash;as opposed to "eager-loaded" modules that are required by the root module, and are thus loaded on launch.
Similarly, the [router](guide/glossary#router) can load child views only when the parent view is activated, and you can build custom elements that can be loaded into an Angular app when needed.
## Lifecycle hook
An interface that allows you to tap into the lifecycle of [directives](guide/glossary#directive) and [components](guide/glossary#component) as they are created, updated, and destroyed.
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 named `ngOnInit`.
@ -454,118 +386,95 @@ Angular calls these hook methods in the following order:
* `ngAfterViewChecked`: after every check of a component's views.
* `ngOnDestroy`: just before the directive is destroyed.
Read more in the [Lifecycle Hooks](guide/lifecycle-hooks) page.
To learn more, see the [Lifecycle Hooks](guide/lifecycle-hooks) page.
{@a M}
## Module
<div class="alert is-important">
In general, a module collects a block of code dedicated to a single purpose. Angular uses standard JavaScript modules, and also defines an Angular module, `NgModule`.
In JavaScript (ECMAScript), each file is a module and all objects defined in the file belong to that module. Objects can exported, making them public, and public objects can be imported for use by other modules.
Angular has the following types of modules:
Angular ships as a collection of JavaScript modules, or libraries. Each Angular library name begins with the `@angular` prefix. Install them with the NPM package manager and import parts of them with JavaScript `import` declarations.
* [NgModules](guide/glossary#ngmodule).
For details and examples, see the [NgModules](guide/ngmodules) page.
* ES2015 modules, as described in this section.
For a comparison, see [JavaScript Modules vs. NgModules](guide/ngmodule-vs-jsmodule).
</div>
A cohesive block of code dedicated to a single purpose.
Angular apps are modular.
In general, you assemble an application from many modules, both the ones you write and the ones you acquire from others.
A module *exports* something of value in that code, typically one thing such as a class;
a module that needs that class *imports* it.
The structure of NgModules and the import/export syntax
is based on the [ES2015 module standard](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 doesn't include a module loader and doesn't have a preference
for any particular third-party library.
You can use 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/packages/common/src/pipes/date_pipe.ts)
class belongs to a feature module named `date_pipe` in the file `date_pipe.ts`.
You rarely access Angular feature modules directly. You usually import them from an Angular [scoped package](guide/glossary#scoped-package) such as `@angular/core`.
Compare the Angular [NgModule](guide/glossary#ngmodule).
{@a N}
{@a ngmodule}
## NgModule
Helps you organize an application into cohesive blocks of functionality.
An NgModule identifies the components, directives, and pipes that the application uses along with the list of external NgModules that the application needs, such as `FormsModule`.
A class definition with an `@NgModule` [decorator](guide/glossary#decorator), that declares and serves as a manifest for a block of code dedicated to an application domain, a workflow, or a closely related set of capabilities.
Every Angular application has an application root-module class. By convention, the class is
called `AppModule` and resides in a file named `app.module.ts`.
Like a [JavaScript module](guide/glossary#module), an NgModule can export functionality for use by other NgModules, and import public functionality from other NgModules.
For details and examples, see [NgModules](guide/ngmodules) and the
related files in that section.
The metadata for an NgModule class collects components, directives, and pipes that the application uses along with the list of imports and exports. See also [Declarable](guide/glossary#declarable).
NgModules are typically named after the file in which the exported thing is defined; for example, the Angular [DatePipe](api/common/DatePipe) class belongs to a feature module named `date_pipe` in the file `date_pipe.ts`. You import them from an Angular [scoped package](guide/glossary#scoped-package) such as `@angular/core`.
Every Angular application has a root module. By convention, the class is called `AppModule` and resides in a file named `app.module.ts`.
To learn more, see the [NgModules](guide/ngmodules) guide.
{@a O}
{@a observable}
## Observable
An subscribable message publisher, which provides multiple items that arrive asynchronously over time.
Observables help you manage asynchronous data, such as data coming from a backend service.
Observables are used within Angular itself, including Angular's event system and its HTTP client service.
A producer of multiple values, which it pushes to [subscribers](guide/glossary#subscriber). Used for asynchronous event handling throughout Angular. You execute an observable by subscribing to it with its `subscribe()` method, passing callbacks for notifications of new values, errors, or completion.
Observables are a proposed feature for ES2016, the next version of JavaScript.
Currently, Angular depends on a third-party library called Reactive Extensions (RxJS) to provide observables.
Observables can deliver single or multiple values of any type to subscribers, either synchronously (as a function delivers a value to its caller), or on a schedule. A subscriber receives notification of new values as they are produced, and of either error or normal completion.
For more information, see the [Observables guide](guide/observables).
Angular uses a third-party library called [Reactive Extensions (RxJS)](http://reactivex.io/rxjs/).
To learn more, see the [Observables](guide/glossary#observable) guide.
{@a observer}
## Observer
An object passed to the `subscribe()` method for an [observable](guide/glossary#observable) that defines the callbacks for the [subscriber](guide/glossary#subscriber).
## Output
A directive property that can be the *target* of event binding
(read more in the [event binding](guide/template-syntax#event-binding)
section of the [Template Syntax](guide/template-syntax) page).
Events stream *out* of this property to the receiver identified
in the template expression to the right of the equal sign.
When defining a [directive](guide/glossary#directive), the `@Output` decorator on a directive property makes that property available as a *target* of [event binding](guide/template-syntax#event-binding).
See the [Input and output properties](guide/template-syntax#inputs-outputs) section of the [Template Syntax](guide/template-syntax) page.
Events stream *out* of this property to the receiver identified
in the [template expression](guide/glossary#template-expression) to the right of the equal sign.
To learn more, see [input and output properties](guide/template-syntax#inputs-outputs).
{@a P}
## Pipe
An Angular pipe is a function that transforms input values to output values for
display in a [view](guide/glossary#view).
Here's an example that uses the built-in `currency` pipe to display
a numeric value in the local currency.
A class with the `@Pipe` decorator which defines a function that transforms input values to output values for display in a [view](guide/glossary#view).
Angular defines various pipes, and you can define new pipes.
<code-example language="html" escape="html">
<label>Price: </label>{{product.price | currency}}
To learn more, see the [pipes](guide/pipes) page.
</code-example>
## Polyfill
You can also write your own custom pipes.
Read more in the page on [pipes](guide/pipes).
An [NPM package](guide/npm-packages) that plugs gaps in a browser's JavaScript implementation. See the [Browser Support](guide/browser-support) guide for polyfills that support particular functionality for particular platforms.
## Provider
A _provider_ creates a new instance of a dependency for the
[dependency injection](guide/glossary#dependency-injection) system.
It relates a lookup token to code&mdash;sometimes called a "recipe"&mdash;that can create a dependency value.
A provider of an injectable service&mdash;specifically, a code recipe associated with a [DI token](guide/glossary#token), which an [injector](guide/glossary#injector) uses to create a new instance of a dependency for a class that requires it.
Angular registers its own providers with every injector, for services that Angular defines. You can register your own providers for services that your app needs.
See also [Service](guide/glossary#service), [Dependency Injection](guide/glossary#di).
{@a Q}
@ -589,24 +498,13 @@ Reactive forms are powerful, flexible, and a good choice for more complex data-e
## Router
Most applications consist of many screens or [views](guide/glossary#view).
The user navigates among them by clicking links and buttons,
and performing other similar actions that cause the application to
replace one view with another.
A tool that configures and implements navigation among states and [views](guide/glossary#view) within an Angular app.
The Angular component router is a richly featured mechanism for configuring and managing the entire view navigation process, including the creation and destruction
of views.
The Router module is an [NgModule](guide/glossary#ngmodule) that provides the necessary service providers and directives for navigating through application views. A [routing component](guide/glossary#routing-component) is one that imports the Router module and whose template contains a `RouterOutlet` element where it can display views produced by the router.
In most cases, components become attached to a router by means
of a `RouterConfig` that defines routes to views.
The Router defines navigation among views on a single page, as opposed to navigation among pages. It interprets URL-like links to determine which views to create or destroy, and which components to load or unload. It allows you to take advantage of [lazy-loading](guide/glossary#lazy-load) in your Angular apps.
A [routing component's](guide/glossary#routing-component) template has a `RouterOutlet` element
where it can display views produced by the router.
Other views in the application likely have anchor tags or buttons with `RouterLink`
directives that users can click to navigate.
For more information, see the [Routing & Navigation](guide/router) page.
To learn more, see the [Routing & Navigation](guide/router) guide.
## Router module
@ -615,6 +513,9 @@ A separate [NgModule](guide/glossary#ngmodule) that provides the necessary servi
For more information, see the [Routing & Navigation](guide/router) page.
## Router outlet
A directive that acts as a placeholder in a routing component's template, which Angular dynamically fills based on the current router state.
## Routing component
@ -627,16 +528,10 @@ For more information, see the [Routing & Navigation](guide/router) page.
## Scoped package
A way to group related *npm* packages.
Read more at the [npm-scope](https://docs.npmjs.com/misc/scope) page.
NgModules are delivered within *scoped packages* such as `@angular/core`,
`@angular/common`, `@angular/platform-browser-dynamic`, `@angular/http`, and `@angular/router`.
Import a scoped package the same way that you import a normal package.
The only difference, from a consumer perspective,
is that the scoped package name begins with the Angular *scope name*, `@angular`.
A way to group related NPM packages.
NgModules are delivered within *scoped packages* whose names begin with the Angular *scope name* `@angular`. For example, `@angular/core`, `@angular/common`, `@angular/http`, and `@angular/router`.
Import a scoped package in the same way that you import a normal package.
<code-example path="architecture/src/app/app.component.ts" linenums="false" title="architecture/src/app/app.component.ts (import)" region="import">
@ -645,20 +540,12 @@ is that the scoped package name begins with the Angular *scope name*, `@angular`
## Service
For data or logic that is not associated
with a specific view or that you want to share across components, build services.
In Angular, a service is a class with the [@Injectable](guide/glossary#injectable) decorator that encapsulates non-UI logic and code that can be re-used across an application.
Angular distinguishes components from services in order to increase modularity and reusability.
Applications often require services such as a hero data service or a logging service.
A service is a class with a focused purpose.
You often create a service to implement features that are
independent from any specific view,
provide shared data or logic across components, or encapsulate external interactions.
Applications often require services such as a data service or a logging service.
For more information, see the [Services](tutorial/toh-pt4) page of the [Tour of Heroes](tutorial) tutorial.
The `@Injectable` metadata allows the service class to be used with the [dependency injection](guide/glossary#di) mechanism. The injectable class is instantiated by a [provider](guide/glossary#provider), and a module maintains a list of providers that can provide a particular type of service as needed by components or other services that require it.
To learn more, see [Introduction to Services](guide/architecture-services).
{@a structural-directive}
@ -668,21 +555,35 @@ For more information, see the [Services](tutorial/toh-pt4) page of the [Tour of
## Structural directives
A category of [directive](guide/glossary#directive) that can
shape or reshape HTML layout, typically by adding and removing elements in the DOM.
The `ngIf` "conditional element" directive and the `ngFor` "repeater" directive are well-known examples.
A category of [directive](guide/glossary#directive) that is responsible for shaping or reshaping HTML layout by modifying the DOM (adding, removing, or manipulating elements and their children).
Read more in the [Structural Directives](guide/structural-directives) page.
To learn more, see the [Structural Directives](guide/structural-directives) page.
{@a subscriber}
## Subscriber
A function that defines how to obtain or generate values or messages to be published. This function is executed when a consumer calls the `subscribe()` method of an [observable](guide/glossary#observable).
The act of subscribing to an observable triggers its execution, associates callbacks with it, and creates a `Subscription` object that lets you unsubscribe.
The `subscribe()` method takes a JavaScript object (called an "observer") with up to three callbacks, one for each type of notification that an observable can deliver:
- The `next` notification: sends a value such as a Number, a String, an Object, etc.
- The `error` notification sends a JavaScript Error or exception.
- The `complete` notification does not send a value, but the handler is called when the call completes. Scheduled values can continue to be returned after the call completes.
{@a T}
## Template
A chunk of HTML that Angular uses to render a [view](guide/glossary#view) with
the support and guidance of an Angular [directive](guide/glossary#directive),
most notably a [component](guide/glossary#component).
A template defines how to render a component's [view](guide/glossary#view) in HTML
A template combines straight HTML with Angular [data-binding](guide/glossary#data-binding) syntax, [directives](guide/glossary#directive), and [template expressions](guide/glossary#template-expression) (logical constructs). The Angular elements insert or calculate values that modify the HTML elements before the page is displayed.
A template is associated with a [component](guide/glossary#component) class through `@Component` [decorator](guide/glossary#decorator). The HTML can be provided inline, as the value of the `template` property, or in a separate HTML file linked through the `templateUrl` property.
Additional templates, represented by a `TemplateRef` object, can define alternative or _embedded_ views, which can be referenced from multiple components.
## Template-driven forms
@ -701,6 +602,8 @@ Template-driven forms are convenient, quick, and simple. They are a good choice
Read about how to build template-driven forms
in the [Forms](guide/forms) page.
{@a template-expression}
## Template expression
@ -711,24 +614,27 @@ Read about how to write template expressions
in the [Template expressions](guide/template-syntax#template-expressions) section
of the [Template Syntax](guide/template-syntax) page.
{@a token}
## Token
An opaque identifier used for efficient table lookup. In Angular, a [DI token](guide/glossary#di-token) is used to find [providers](guide/glossary#provider) of dependencies in the [dependency injection](guide/glossary#di) system.
{@a transpile}
## Transpile
The process of transforming code written in one form of JavaScript
(such as TypeScript) into another form of JavaScript. (See also [ECMAScript](guide/glossary#ecma)).
The translation process that tranforms one version of JavaScript to another version; for example, down-leveling ES2015 to the older ES5 version.
{@a typescript}
## TypeScript
A version of JavaScript that supports most [ECMAScript 2015](guide/glossary#ecma)
language features such as [decorators](guide/glossary#decorator).
TypeScript is notable for its optional typing system, which provides
compile-time type checking and strong tooling support (such as "intellisense,"
code completion, refactoring, and intelligent search). Many code editors
and IDEs support TypeScript either natively or with plugins.
TypeScript is a programming language notable for its optional typing system, which provides
compile-time type checking and strong tooling support (such as
code completion, refactoring, inline documentation, and intelligent search). Many code editors
and IDEs support TypeScript either natively or with plug-ins.
TypeScript is the preferred language for Angular development. Read more about TypeScript at [typescriptlang.org](http://www.typescriptlang.org/).
@ -739,18 +645,26 @@ TypeScript is the preferred language for Angular development. Read more about Ty
## View
A portion of the screen that displays information and responds
to user actions such as clicks, mouse moves, and keystrokes.
A view is the smallest grouping of display elements that can be created and destroyed together.
Angular renders a view under the control of one or more [directives](guide/glossary#directive),
especially [component](guide/glossary#component) directives and their companion [templates](guide/glossary#template).
The component plays such a prominent role that it's often
convenient to refer to a component as a view.
Views often contain other views. Any view might be loaded and unloaded
dynamically as the user navigates through the application, typically
under the control of a [router](guide/glossary#router).
A view is specifically represented by a `ViewRef` instance associated with the component.
A view that belongs to a component is called a _host view_.
Views are typically collected into [view hierarchies](guide/glossary#view-tree).
Properties of elements in a view can change dynamically, in response to user actions; the structure (number and order) of elements in a view cannot. You can change the structure of elements by inserting, moving, or removing nested views within their view containers.
View hierarchies can be loaded and unloaded dynamically as the user navigates through the application, typically under the control of a [router](guide/glossary#router).
{@a view-tree}
## View hierarchy
A tree of related views that can be acted on as a unit. The root view is a component's _host view_. A host view can be the root of a tree of _embedded views_, collected in a _view container_ (`ViewContainerRef`) attached to an anchor element in the hosting component. The view hierarchy is a key part of Angular change detection.
The view hierarchy does not imply a component hierarchy. Views that are embedded in the context of a particular hierarchy can be host views of other components. Those components can be in the same NgModule as the hosting component, or belong to other NgModules.
{@a W}
@ -769,21 +683,11 @@ See [Custom element](guide/glossary#custom-element)
## Zone
A mechanism for encapsulating and intercepting
a JavaScript application's asynchronous activity.
An execution context for a set of asynchronous tasks. Useful for debugging, profiling, and testing apps that include asynchronous operations such as event processing, promises, and calls to remote servers.
The browser DOM and JavaScript have a limited number
of asynchronous activities, such as DOM events (for example, 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.
An Angular app runs in a zone where it can respond to asynchronous events by checking for data changes and updating the information it displays by resolving [data bindings](guide/glossary#data-binding).
Zones intercept all of these activities and give a "zone client" the opportunity
to take action before and after the async activity finishes.
Angular runs your application in a zone where it can respond to
asynchronous events by checking for data changes and updating
the information it displays via [data bindings](guide/glossary#data-binding).
A zone client can take action before and after an async operation completes.
Learn more about zones in this
[Brian Ford video](https://www.youtube.com/watch?v=3IqtmUscE_U).