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#### Docs

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  - 1. The Hero Editor
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# Glossary

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

This glossary lists the most prominent terms and a few less familiar ones that have unusual or unexpected definitions.

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

## Ahead-of-time (AOT) compilation

AngularDart apps are compiled at build time (ahead of time), rather than at run time (just in time).

## Annotation

When unqualified, annotation refers to a Dart metadata annotation (as opposed to, say, a type annotation). A metadata annotation begins with the character `@`, followed by either a reference to a compile-time constant (such as `Component`) or a call to a constant constructor. See the metadata section of the Dart language tour for details.

The corresponding term in TypeScript and JavaScript is decorator.

## Attribute directive

A category of 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.

For example, you can use the `ngClass` directive to add and remove CSS class names.

Learn about them in the Attribute Directives guide.

## Binding

Usually refers to data binding and the act of binding an HTML object property to a data object property.

Sometimes refers to a dependency-injection binding between a “token”—also referred to as a “key”—and a dependency provider.

## Bootstrap

To initialize and launch an Angular app.

You launch an Angular app using the runApp() function. In that function, you identify the app’s root component, which is the first component that is loaded for the app. You can optionally register service providers with the dependency injection system. For more information, see the Setup page.

## camelCase

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 lowercase.

Function, property, and method names are typically spelled in camelCase. For example, `square`, `firstName`, and `getHeroes`. Notice that `square` is an example of how you write a single word in camelCase.

camelCase is also known as lower camel case to distinguish it from upper camel case, or PascalCase. In Angular documentation, “camelCase” always means lower camel case.

## Component

An Angular class responsible for exposing data to a 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 with a companion template.

Apply the `@Component` annotation 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.

Those familiar with “MVC” and “MVVM” patterns will recognize the component in the role of “controller” or “view model”.

## dash-case

The practice of writing compound words or phrases such that each word is separated by a dash or hyphen (`-`). This form is also known as kebab-case.

Directive selectors (like `my-app`) are often spelled in dash-case.

## Data binding

Apps display data values to a user and respond to user actions (such as clicks, touches, and keystrokes).

In data binding, you declare the relationship between an HTML widget and data source and let the framework handle the details. Data binding is an alternative to manually pushing app data values into HTML, attaching event listeners, pulling changed values from the screen, and updating app 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 page:

- Interpolation.
- Property binding.
- Event binding.
- Attribute binding.
- Class binding.
- Style binding.
- Two-way data binding with ngModel.

## Decorator | decoration

JavaScript terms that, in this documentation, refer to an annotation.

## Dependency injection

A design pattern and mechanism for creating and delivering parts of an app to other parts of an app that request them.

Angular developers prefer to build apps by defining many simple parts that each do one thing well and then wiring them together at runtime.

These parts often rely on other parts. An Angular 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”.

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”.

Angular provides and relies upon its own sophisticated dependency-injection system to assemble and run apps by “injecting” app parts into other app parts where and when needed.

At the core, an `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 (`OpaqueToken`). 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` 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 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 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 directive is usually associated with an HTML element or attribute. This element or attribute is often referred to as the directive itself.

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.

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.

Directives fall into one of the following categories:

- Components combine application logic with an HTML template to render app views. Components are usually represented as HTML elements. They are the building blocks of an Angular app.

- Attribute directives 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.

- Structural directives are responsible for shaping or reshaping HTML layout, typically by adding, removing, or manipulating elements and their children.

## ECMAScript

The official JavaScript language specification.

## ES2015

Short hand for ECMAScript 2015.

## ES5

Short hand for ECMAScript 5, the version of JavaScript run by most modern browsers.

## ES6

Short hand for ECMAScript 2015.

## Injector

An object in the Angular dependency-injection system that can find a named dependency in its cache or create a dependency with a registered provider.

## Input

A directive property that can be the target of a property binding (explained in detail in the 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.

See the Input and output properties section of the Template Syntax page.

## Interpolation

A form of property data binding in which a 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.

    <label>My current hero is {{hero.name}}</label>

Read more about interpolation in the Template Syntax page.

## Just-in-time (JIT) compilation

A way (no longer supported) of compiling components in the browser and launching apps dynamically. As of v5, AngularDart supports only ahead-of-time compilation.

## kebab-case

See dash-case.

## Lifecycle hooks

Directives and components have a lifecycle managed by Angular as it creates, updates, and destroys them.

You 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 named `ngOnInit`.

Angular calls these hook methods in the following order:

- `ngAfterChanges`: when an input/output binding value changes.
- `ngOnInit`: after the first `ngAfterChanges`.
- `ngDoCheck`: developer’s custom change detection.
- `ngAfterContentInit`: after component content initialized.
- `ngAfterContentChecked`: after every check of component content.
- `ngAfterViewInit`: after a component’s views are initialized.
- `ngAfterViewChecked`: after every check of a component’s views.
- `ngOnDestroy`: just before the directive is destroyed.

Read more in the Lifecycle Hooks page.

## Module

In this documentation, the term module refers to a Dart compilation unit, such as a library or package. If a Dart file has no `library` or `part` directive, then that file itself is a library and thus a compilation unit. For more information about compilation units, see the Libraries and Scripts chapter in the Dart Language Specification.

## Output

A directive property that can be the target of event binding (read more in the event binding section of the Template Syntax page). Events stream out of this property to the receiver identified in the template expression to the right of the equal sign.

See the Input and output properties section of the Template Syntax page.

## PascalCase

The practice of writing individual words, compound words, or phrases such that each word or abbreviation begins with a capital letter. Class names are typically spelled in PascalCase. For example, `Person` and `HeroDetailComponent`.

This form is also known as upper camel case to distinguish it from lower camel case or simply camelCase. In this documentation, “PascalCase” means upper camel case and “camelCase” means lower camel case.

## Pipe

An Angular pipe is a function that transforms input values to output values for display in a view. Here’s an example that uses the built-in `currency` pipe to display a numeric value in the local currency.

    <label>Price:</label>{{product.price | currency}}

You can also write your own custom pipes. Read more in the page on pipes.

## Provider

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.

## Router

Most apps consist of many screens or views. The user navigates among them by clicking links and buttons, and performing other similar actions that cause the app to replace one view with another.

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.

## Routing component

An Angular component with a `RouterOutlet` that displays views based on router navigations.

For more information, see the Routing & Navigation page.

## Service

For data or logic that is not associated with a specific view or that you want to share across components, build services.

Apps 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.

Apps often require services such as a data service or a logging service.

For more information, see the Services page of the Tour of Heroes tutorial.

## snake_case

The practice of writing compound words or phrases such that an underscore (`_`) separates one word from the next. This form is also known as underscore case.

Dart package names and filenames are spelled in snake_case, by convention. For example, `angular_tour_of_heroes` and `app_component.dart`.

## Structural directive

A category of 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.

Read more in the Structural Directives page.

## Template

A chunk of HTML that Angular uses to render a view with the support and guidance of an Angular directive, most notably a component.

## Template expression

A Dart-like syntax that Angular evaluates within a data binding.

Read about how to write template expressions in the Template expressions section of the Template Syntax page.

## Transpile

The process of transforming code written in one language (for example, Dart or TypeScript) into another (such as ES5).

## TypeScript

A version of JavaScript that supports most ECMAScript 2015 language features such as decorators. Read more about TypeScript at typescriptlang.org.

## View

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, especially component directives and their companion templates. 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 app, typically under the control of a router.

## Zone

Zones are a mechanism for encapsulating and intercepting a Dart app’s asynchronous activity.

Read more about zones in this article.