Glossary

Send feedback

Angular has a vocabulary of its own. Most Angular terms are everyday 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

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 Dart Language Guide 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.

A good example of an attribute directive is the ngClass directive for adding and removing CSS class names.

Binding

Almost always refers to Data Binding and the act of binding an HTML object property to a data object property.

May refer to a dependency injection binding between a "token", also referred to as a "key", and a dependency provider. This more rare usage should be clear in context.

Bootstrap

You launch an Angular application by "bootstrapping" it with the bootstrap method. Bootstrapping identifies an application's top level "root" component, which is the first component that is loaded for the application, and optionally registers service providers with the dependency injection system. For more information, see the Setup page.

You can bootstrap multiple apps in the same index.html, each with its own top level root.

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. Examples: square, firstName, getHeroes.

This form is also known as lower camel case, to distinguish it from upper camel case, which is PascalCase. When you see "camelCase" in this documentation it 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.

You apply the @Component 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".

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) and the root of filenames (such as hero-list.component.ts) are often spelled in dash-case.

Data binding

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

Instead of manually pushing application data values into HTML, attaching event listeners, pulling changed values from the screen, and updating application data values, you can use data binding by declaring the relationship between an HTML widget and data source and let the framework handle the details.

Angular has a rich data binding framework with a variety of data binding operations and supporting declaration syntax.

Read about the forms of binding in the Template Syntax page:

Decorator | decoration

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

Dependency injection

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 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 applications by "injecting" application parts into other application parts where and when needed.

At the core there is an 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). You rarely deal 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. We can register our 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. 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 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 three categories:

  1. Components 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.

  2. Attribute directives 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.

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

ECMAScript

ES2015

Short hand for ECMAScript 2015.

ES6

Short hand for ECMAScript 2015.

ES5

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

Injector

An object in the Angular dependency injection system that can find a named "dependency" in its cache or create such a thing 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.

Read more about interpolation in the Template Syntax page.

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:

  • ngOnChanges - when an input/output binding value changes.
  • 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.

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. 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. Examples: Person, HeroDetailComponent.

This form is also known as upper camel case to distinguish it from lower camel case, which is simply called 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. Use the @Pipe to associate the pipe function with a name. You then use that name in your 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.

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 applications consist of many screens or views. 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.

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.

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. Examples: angular_tour_of_heroes, app_component.dart.

Service

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

Applications often require services such as a hero data service or a logging service.

A service is a class with a focused purpose. We 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.

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

Structural directive

A category of directive that can shape or reshape HTML layout, typically by adding, removing, or manipulating elements and their children; for example, the ngIf "conditional element" directive and the ngFor "repeater" directive.

Read more in the Structural Directives page.

Template

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

Template expression

An expression is a Dart-like syntax that Angular evaluates within a data binding.

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

Transpile

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

TypeScript

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

View

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, 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 and any view might be loaded and unloaded dynamically as the user navigates through the application, typically under the control of a router.

Zone

Zones are a mechanism for encapsulating and intercepting a Dart application's asynchronous activity.

Learn more about zones in this article.