Return to Angular

• Glossary of Angular Terms

Creating a glossary that includes the top 40 Angular framework concepts and tools, sorted by their most commonly used, involves highlighting foundational elements of Angular development. Angular is a platform and framework for building single-page client applications using HTML and TypeScript. It's known for its dependency injection, declarative templates, end-to-end tooling, and integrated best practices to solve development challenges.

Below is a glossary formatted in MediaWiki markup, showcasing essential Angular concepts and tools with examples:

This glossary lists and explains the top 40 Angular framework concepts and tools, focusing on those most commonly used in Angular development. Each entry provides a brief description and code or usage example.

Components are the basic building blocks of Angular applications. They control a patch of screen called a view.

@Component({
  selector: 'app-root',
  templateUrl: './app.component.html',
  styleUrls: ['./app.component.css']
})
export class AppComponent {
  title = 'angular-app';
}

Angular modules (NgModule) help organize an application into cohesive blocks of functionality.

@NgModule({
  declarations: [
    AppComponent
  ],
  imports: [
    BrowserModule
  ],
  providers: [],
  bootstrap: [AppComponent]
})
export class AppModule { }

Templates define views in Angular. They are written with HTML that contains Angular-specific elements and attributes.

<p>{{ title }}</p>

Metadata decorates a class so that Angular knows what to do with it. Use decorators to add metadata.

@Component({
  selector: 'app-example',
  templateUrl: './example.component.html'
})

Data binding is the mechanism to coordinate parts of a template with parts of a component.

<input [(ngModel)]="name" placeholder="Enter name">

Directives modify the layout and behavior of DOM elements.

<p *ngIf="condition">Content to render conditionally.</p>

Services are singleton objects that provide functionality for various Angular components.

@Injectable({
  providedIn: 'root'
})
export class ExampleService {
}

Angular's dependency injection system provides dependencies to components and services.

constructor(private exampleService: ExampleService) { }

The Angular Router enables navigation from one view to the next as users perform application tasks.

const routes: Routes = [
  { path: 'home', component: HomeComponent }
];

HttpClient is Angular's mechanism for communicating with a remote server over HTTP.

this.http.get('/api/items').subscribe(data => {
  console.log(data);
});

Angular provides two approaches to forms: reactive forms and template-driven forms.

<form [formGroup]="myForm">
  <input formControlName="firstName">
</form>

Pipes transform displayed values within a template.

<p>The hero's birthday is {{ birthday | date }}</p>

Observables provide support for passing messages between parts of your application.

this.exampleService.getData().subscribe(data => this.data = data);

Lifecycle hooks allow you to tap into the lifecycle of directives and components.

ngOnInit(): void {
  console.log('Component initialized');
}

Angular's animation system lets you define animations in your applications.

animations: [
  trigger('openClose', [
    state('open', style({
      height: '200px',
      opacity: 1,
      backgroundColor: 'yellow'
    })),
    state('closed', style({
      height: '100px',
      opacity: 0.5,
      backgroundColor: 'green'
    })),
    transition('open => closed', [
      animate('1s')
    ]),
    transition('closed => open', [
      animate('0.5s')
    ]),
  ]),
]

The Angular CLI is a command-line interface tool that you use to initialize, develop, scaffold, and maintain Angular applications. Usage example: ``` ng generate component my-new-component ```

Angular Material provides modern UI components for Angular applications. Usage example: ``` import {MatButtonModule} from '@angular/material/button'; ```

Lazy loading is a technique in Angular that allows you to load JavaScript components asynchronously when a specific route is activated.

const routes: Routes = [
  {
    path: 'feature',
    loadChildren: () => import('./feature/feature.module').then(m => m.FeatureModule)
  }
];

RxJS is a library for composing asynchronous and event-based programs

by using observable sequences.

import { of } from 'rxjs';
of(1, 2, 3).subscribe(x => console.log(x));

Angular Universal is a technology that renders Angular applications on the server. Usage example: ``` ng add @nguniversal/express-engine ```

AOT compilation converts Angular HTML and TypeScript code into efficient JavaScript code during the build phase before the browser downloads and runs that code. Usage example: ``` ng build –aot ```

Zone.js is a library that Angular uses for detecting and debugging asynchronous operations.

// Example usage in Angular context

Angular's change detection mechanism automatically updates the DOM when your model changes.

@Component({
  changeDetection: ChangeDetectionStrategy.OnPush,
  selector: 'app-cmp',
  templateUrl: './app.component.html'
})

The `ngModel` directive binds an HTML form element to a property on the scope.

<input [(ngModel)]="name">

Interceptors are a way to do preprocessing and postprocessing of HTTP requests and responses.

@Injectable()
export class MyInterceptor implements HttpInterceptor {
  intercept(req: HttpRequest<any>, next: HttpHandler): Observable<HttpEvent<any>> {
    // Modify request here
    return next.handle(req);
  }
}

Structural directives change the DOM layout by adding and removing DOM elements.

<div *ngIf="condition">Show this div if condition is true</div>

Attribute directives change the appearance or behavior of an element, component, or another directive.

<button [ngStyle]="{color: 'red'}">Red Button</button>

Providers define how the injector can be created for an NgModule.

@NgModule({
  providers: [ExampleService]
})

Event binding allows you to listen to events such as keystrokes, mouse movements, clicks, and touches.

<button (click)="onClick()">Click me</button>

Property binding in Angular helps you set values for properties of HTML elements.

<img [src]="userImageUrl">

Two-way binding gives your app a way to share data between a component class and its template.

<input [(ngModel)]="user.name">

Angular provides testing utilities like Jasmine and Karma for unit testing components and services.

it('should create', () => {
  expect(component).toBeTruthy();
});

Decorators are design patterns that are used to separate modification or decoration of a class without modifying the original source code.

@Injectable({
  providedIn: 'root'
})
export class MyService {
}

Dynamic components are components that are created dynamically at runtime in Angular applications.

@Component({
  entryComponents: [MyDynamicComponent]
})

This glossary covers foundational Angular concepts and tools, providing a solid foundation for understanding and utilizing Angular's capabilities in web development.

This overview captures essential Angular features and tools, offering insights into Angular's capabilities for developers looking to build dynamic and responsive web applications.

Angular has its own Angular vocabulary. Most Angular terms are common English words or computing terms that have a specific meaning within the Angular system.

This glossary of Angular vocabular lists the most prominent Angular terms and a few less familiar ones with unusual or unexpected definitions.

• ahead-of-time (AOT) compilation - The Angular ahead-of-time (AOT) compiler converts Angular HTML and TypeScript code into efficient JavaScript code during the build phase. The build phase occurs before the browser downloads and runs the rendered code. This is the best compilation mode for production environments, with decreased load time and increased performance compared to just-in-time (JIT) compilation.

By compiling your application using the ngc command-line tool, you can bootstrap directly to a module factory, so you do not need to include the Angular compiler in your JavaScript bundle.

• Angular element - An Angular component packaged as a custom element.

Learn more in Angular Elements Overview

• Angular package format (APF) - An Angular specific specification for layout of npm packages that is used by all first-party Angular packages, and most third-party Angular libraries.

Learn more in the Angular Package Format specification.

• Angular annotation - A structure that provides metadata for a class. To learn more, see decorator.

• Angular app-shell - App shell is a way to render a portion of your application using a route at build time. This gives users a meaningful first paint of your application that appears quickly because the browser can render static HTML and CSS without the need to initialize JavaScript. To learn more, see The App Shell Model.

You can use the Angular CLI to generate an app shell. This can improve the user experience by quickly launching a static rendered page while the browser downloads the full client version and switches to it automatically after the code loads. A static rendered page is a skeleton common to all pages. To learn more, see Service Worker and PWA.

• Angular Architect - The tool that the Angular CLI uses to perform complex tasks such as compilation and test running, according to a provided configuration. Architect is a shell that runs a builder with a given target configuration. The builder is defined in an npm package.

In the workspace configuration file, an “architect” section provides configuration options for Architect builders.

For example, a built-in builder for linting is defined in the package @angular-devkit/build_angular:tslint, which uses the TSLint tool to perform linting, with a configuration specified in a tslint.json file.

Use the ng run Angular CLI command to invoke a builder by specifying a target configuration associated with that builder. Integrators can add builders to enable tools and workflows to run through the Angular CLI. For example, a custom builder can replace the third-party tools used by the built-in implementations for Angular CLI commands, such as ng build or ng test.

• Angular 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.

Learn more in Attribute Directives.

• Angular binding - Generally, the practice of setting a variable or property to a data value. Within Angular, typically refers to data binding, which coordinates DOM object properties with data object properties.

Sometimes refers to a Angular dependency-injection binding between an Angular token and an Angular dependency provider.

• Angular bootstrap - A way to initialize and launch an application or system.

In Angular, the AppModule root NgModule of an application has a bootstrap property that identifies the top-level components of the application. During the bootstrap process, Angular creates and inserts these components into the index.html host web page. You can bootstrap multiple applications in the same index.html. Each application contains its own components.

Learn more in Angular Bootstrapping.

• Angular builder - A function that uses the Architect API to perform a complex process such as build or test. The builder code is defined in an npm package.

For example, BrowserBuilder runs a webpack build for a browser target and KarmaBuilder starts the Karma server and runs a webpack build for unit tests.

The ng run Angular CLI command invokes a builder with a specific target configuration. The workspace configuration file, angular.json, contains default configurations for built-in builders.

• Angular case types - Angular uses capitalization conventions to distinguish the names of various types, as described in the naming guidelines section of the Style Guide. Here is a summary of the case types:

DETAILS EXAMPLE camelCase Symbols, properties, methods, pipe names, non-component directive selectors, constants. Standard or lower camel case uses lowercase on the first letter of the item. selectedHero UpperCamelCase PascalCase Class names, including classes that define components, interfaces, NgModules, directives, and pipes. Upper camel case uses uppercase on the first letter of the item. HeroComponent dash-case kebab-case Descriptive part of file names, component selectors. app-hero-list underscore_case snake_case Not typically used in Angular. Snake case uses words connected with underscores. convert_link_mode UPPER_UNDERSCORE_CASE UPPER_SNAKE_CASE SCREAMING_SNAKE_CASE Traditional for constants. This case is acceptable, but camelCase is preferred. Upper snake case uses words in all capital letters connected with underscores. FIX_ME change detection The mechanism by which the Angular framework synchronizes the state of the UI of an application with the state of the data. The change detector checks the current state of the data model whenever it runs, and maintains it as the previous state to compare on the next iteration.

As the application logic updates component data, values that are bound to DOM properties in the view can change. The change detector is responsible for updating the view to reflect the current data model. Similarly, the user can interact with the UI, causing events that change the state of the data model. These events can trigger change detection.

Using the default change-detection strategy, the change detector goes through the view hierarchy on each VM turn to check every data-bound property in the template. In the first phase, it compares the current state of the dependent data with the previous state, and collects changes. In the second phase, it updates the page DOM to reflect any new data values.

If you set the OnPush change-detection strategy, the change detector runs only when explicitly invoked, or when it is triggered by an Input reference change or event handler. This typically improves performance. To learn more, see Optimize the change detection in Angular.

class decorator A decorator that appears immediately before a class definition, which declares the class to be of the given type, and provides metadata suitable to the type.

The following decorators can declare Angular class types.

@Component() @Directive() @Pipe() @Injectable() @NgModule() class field decorator A decorator statement immediately before a field in a class definition that declares the type of that field. Some examples are @Input and @Output.

collection In Angular, a set of related schematics collected in an npm package.

command-line interface (CLI) The Angular CLI is a command-line tool for managing the Angular development cycle. Use it to create the initial filesystem scaffolding for a workspace or project, and to run schematics that add and modify code for initial generic versions of various elements. The Angular CLI supports all stages of the development cycle, including building, testing, bundling, and deployment.

To begin using the Angular CLI for a new project, see Local Environment Setup. To learn more about the full capabilities of the Angular CLI, see the Angular CLI command reference. See also Schematics CLI.

component A class with the @Component() decorator that associates it with a companion template. Together, the component class and template define a view. A component is a special type of directive. The @Component() decorator extends the @Directive() decorator with template-oriented features.

An Angular component class is responsible for exposing data and handling most of the display and user-interaction logic of the view through data binding.

Read more about component classes, templates, and views in Introduction to Angular concepts.

configuration See workspace configuration

content projection A way to insert DOM content from outside a component into the view of the component in a designated spot.

To learn more, see Responding to changes in content.

custom element A web platform feature, currently supported by most browsers and available in other browsers through polyfills. See Browser support.

The custom element feature extends HTML by allowing you to define a tag whose content is created and controlled by JavaScript code. A custom element is recognized by a browser when it is added to the CustomElementRegistry. A custom element is also referenced as a web component.

You can use the API to transform an Angular component so that it can be registered with the browser and used in any HTML that you add directly to the DOM within an Angular application. The custom element tag inserts the view of the component, with change-detection and data-binding functionality, into content that would otherwise be displayed without Angular processing. See Angular element. See also dynamic component loading.

data binding A process that allows applications to display data values to a user and respond to user actions. User actions include clicks, touches, keystrokes, and so on.

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

Read about the following forms of binding of the Template Syntax in Angular:

Interpolation Property binding Event binding Attribute binding Class and style binding Two-way data binding with ngModel declarable A class that you can add to the declarations list of an NgModule. You can declare components, directives, and pipes, unless they have the standalone flag in their decorators set to true, which makes them standalone. Note: standalone components/directives/pipes are not declarables. More info about standalone classes can be found below.

Do not declare the following:

A class already declared as standalone. A class that is already declared in another NgModule. An array of directives imported from another package. For example, do not 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. Note that declarables can also be declared as standalone and simply be imported inside other standalone components or existing NgModules, to learn more, see the Standalone components guide.

decorator | decoration A function that modifies a class or property definition. Decorators are an experimental (stage 3) JavaScript language feature. A decorator is also referenced as an annotation. TypeScript adds support for decorators.

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.

To learn more, see class decorator. See also class field decorator.

dependency injection (DI) A design pattern and mechanism for creating and delivering some parts of an application (dependencies) to other parts of an application that require them.

In Angular, dependencies are typically services, but they also can be values, such as strings or functions. An injector for an application (created automatically during bootstrap) instantiates dependencies when needed, using a configured provider of the service or value. Learn more in Dependency Injection in Angular.

DI token A lookup token associated with a dependency provider, for use with the dependency injection system.

directive A class that can modify the structure of the DOM or modify attributes in the DOM and component data model. A directive class definition is immediately preceded by a @Directive() decorator that supplies metadata.

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, it creates the matching directive class instance and gives the instance control over that portion of the browser DOM.

Angular has three categories of directive:

Components use @Component() to associate a template with a class. @Component() is an extension of @Directive().

Attribute directives modify behavior and appearance of page elements.

Structural directives modify the structure of the DOM.

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 with a custom directive; this extends the template syntax that you can use in your applications. A selector is an HTML tag, such as <my-directive>.

UpperCamelCase, such as NgIf, refers to a directive class. You can use UpperCamelCase when describing properties and directive behavior.

lowerCamelCase, such as ngIf refers to the attribute name of a directive. You can use lowerCamelCase when describing how to apply the directive to an element in the HTML template.

domain-specific language (DSL) A special-purpose library or API. To learn more, see Domain-specific language. Angular extends TypeScript with domain-specific languages for a number of domains relevant to Angular applications, defined in NgModules such as animations, forms, and routing and navigation.

dynamic component loading A technique for adding a component to the DOM at run time. Requires that you exclude the component from compilation and then connect it to the change-detection and event-handling framework of Angular when you add it to the DOM.

See also custom element, which provides an easier path with the same result.

eager loading NgModules or components that are loaded on launch are referenced as eager-loaded, to distinguish them from those that are loaded at run time that are referenced as lazy-loaded. See also lazy loading.

ECMAScript The official JavaScript language specification.

Not all browsers support the latest ECMAScript standard, but you can use a transpiler to write code using the latest features, which will then be transpiled to code that runs on versions that are supported by browsers. An example of a transpiler is TypeScript. To learn more, see Browser Support.

element Angular defines an ElementRef class to wrap render-specific native UI elements. In most cases, this allows you to use Angular templates and data binding to access DOM elements without reference to the native element.

The documentation generally refers to elements as distinct from DOM elements. Elements are instances of a ElementRef class. DOM elements are able to be accessed directly, if necessary.

To learn more, see also custom element.

entry point A JavaScript module that is intended to be imported by a user of an npm package. An entry-point module typically re-exports symbols from other internal modules. A package can contain multiple entry points. For example, the @angular/core package has two entry-point modules, which can be imported using the module names @angular/core and @angular/core/testing.

form control An instance of FormControl, which is a fundamental building block for Angular forms. Together with FormGroup and FormArray, tracks the value, validation, and status of a form input element.

Read more forms in the Introduction to forms in Angular.

form model The “source of truth” for the value and validation status of a form input element at a given point in time. When using reactive forms, the form model is created explicitly in the component class. When using template-driven forms, the form model is implicitly created by directives.

Learn more about reactive and template-driven forms in the Introduction to forms in Angular.

form validation A check that runs when form values change and reports whether the given values are correct and complete, according to the defined constraints. Reactive forms apply validator functions. Template-driven forms use validator directives.

To learn more, see Form Validation.

immutability The inability to alter the state of a value after its creation. Reactive forms perform immutable changes in that each change to the data model produces a new data model rather than modifying the existing one. Template-driven forms perform mutable changes with NgModel and two-way data binding to modify the existing data model in place.

injectable An Angular class or other definition that provides a dependency using the dependency injection mechanism. An injectable service class must be marked by the @Injectable() decorator. Other items, such as constant values, can also be injectable.

injector An object in the Angular dependency-injection system that can find a named dependency in its cache or create a dependency using a configured provider. Injectors are created for NgModules automatically as part of the bootstrap process and are inherited through the component hierarchy.

An injector provides a singleton instance of a dependency, and can inject this same instance in multiple components. A hierarchy of injectors at the NgModule and component level can provide different instances of a dependency to their own components and child components. You can configure injectors with different providers that can provide different implementations of the same dependency. Learn more about the injector hierarchy in Hierarchical Dependency Injectors.

input When defining a directive, the @Input() decorator on a directive property makes that property available as a target of a property binding. Data values flow into an input property from the data source identified in the template expression to the right of the equal sign.

To learn more, see @Input() and @Output() decorator functions.

interpolation A form of property data binding in which a template expression between double-curly braces 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.

content_copy <label>My current hero is

</label> Read more in the Interpolation guide.

Ivy Ivy is the historical code name for the current compilation and rendering pipeline in Angular. It is now the only supported engine, so everything uses Ivy.

JavaScript To learn more, see ECMAScript. To learn more, see also TypeScript.

just-in-time (JIT) compilation 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 (as opposed to AOT compilation) when you run the ng build and ng serve Angular 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 to ahead-of-time (AOT) compilation.

lazy loading A process that 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. The example differs from eager-loaded modules that are required by the root module and are loaded on launch.

The router makes use of lazy loading to load child views only when the parent view is activated. Similarly, you can build custom elements that can be loaded into an Angular application when needed.

library In Angular, a project that provides functionality that can be included in other Angular applications. A library is not a complete Angular application and cannot run independently.

To add re-usable Angular functionality to non-Angular web applications, use Angular custom elements.

Library developers can use the Angular CLI to generate scaffolding for a new library in an existing workspace, and can publish a library as an npm package. Application developers can use the Angular CLI to add a published library for use with an application in the same workspace. See also schematic.

lifecycle hook An interface that allows you to tap into the lifecycle of directives and components 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.

Angular runs these hook methods in the following order:

HOOK METHOD DETAILS 1 ngOnChanges When an input or output binding value changes. 2 ngOnInit After the first ngOnChanges. 3 ngDoCheck Developer's custom change detection. 4 ngAfterContentInit After component content initialized. 5 ngAfterContentChecked After every check of component content. 6 ngAfterViewInit After the views of a component are initialized. 7 ngAfterViewChecked After every check of the views of a component. 8 ngOnDestroy Just before the directive is destroyed. To learn more, see Lifecycle Hooks.

module 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, or ECMAScript, each file is a module and all objects defined in the file belong to that module. Objects can be exported, making them public, and public objects can be imported for use by other modules.

Angular ships as a collection of JavaScript modules. A collection of JavaScript modules are also referenced as a library. Each Angular library name begins with the @angular prefix. Install Angular libraries with the npm package manager and import parts of them with JavaScript import declarations.

Compare to NgModule.

ngcc Angular compatibility compiler. If you build your application using Ivy, but it depends on libraries that have not been compiled with Ivy, the Angular CLI uses ngcc to automatically update the dependent libraries to use Ivy.

NgModule A class definition preceded by the @NgModule() decorator, which 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.

Like a JavaScript module, an NgModule can export functionality for use by other NgModules and import public functionality from other NgModules. 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.

NgModules are typically named after the file in which the exported thing is defined. For example, the Angular DatePipe class belongs to a feature module named date_pipe in the file date_pipe.ts. You import them from an Angular scoped package such as @angular/core.

Every Angular application has a root module. By convention, the class is named AppModule and resides in a file named app.module.ts.

To learn more, see NgModules.

npm package The npm package manager is used to distribute and load Angular modules and libraries.

Learn more about how Angular uses Npm Packages.

ngc ngc is a Typescript-to-Javascript transpiler that processes Angular decorators, metadata, and templates, and emits JavaScript code. The most recent implementation is internally referred to as ngtsc because it is a minimalistic wrapper around the TypeScript compiler tsc that adds a transform for processing Angular code.

observable A producer of multiple values, which it pushes to subscribers. 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 can deliver in one the following ways a single value or multiple values of any type to subscribers.

Synchronously as a function delivers a value to the requester Scheduled A subscriber receives notification of new values as they are produced and notification of either normal completion or error completion.

Angular uses a third-party library named Reactive Extensions (RxJS). To learn more, see Observables.

observer An object passed to the subscribe() method for an observable. The object defines the callbacks for the subscriber.

output When defining a directive, the @Output{} decorator on a directive property makes that property available as a 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.

To learn more, see @Input() and @Output() decorator functions.

pipe A class which is preceded by the @Pipe{} decorator and which defines a function that transforms input values to output values for display in a view. Angular defines various pipes, and you can define new pipes.

To learn more, see Pipes.

platform In Angular terminology, a platform is the context in which an Angular application runs. The most common platform for Angular applications is a web browser, but it can also be an operating system for a mobile device, or a web server.

Support for the various Angular run-time platforms is provided by the @angular/platform-* packages. These packages allow applications that make use of @angular/core and @angular/common to execute in different environments by providing implementation for gathering user input and rendering UIs for the given platform. Isolating platform-specific functionality allows the developer to make platform-independent use of the rest of the framework.

When running in a web browser, BrowserModule is imported from the platform-browser package, and supports services that simplify security and event processing, and allows applications to access browser-specific features, such as interpreting keyboard input and controlling the title of the document being displayed. All applications running in the browser use the same platform service.

When server-side rendering (SSR) is used, the platform-server package provides web server implementations of the DOM, XMLHttpRequest, and other low-level features that do not rely on a browser.

polyfill An npm package that plugs gaps in the JavaScript implementation of a browser. See Browser Support for polyfills that support particular functionality for particular platforms.

project In the Angular CLI, a standalone application or library that can be created or modified by an Angular CLI command.

A project, as generated by the ng new, contains the set of source files, resources, and configuration files that you need to develop and test the application using the Angular CLI. Projects can also be created with the ng generate application and ng generate library commands.

To learn more, see Project File Structure.

The angular.json file configures all projects in a workspace.

provider An object that implements one of the Provider interfaces. A provider object defines how to obtain an injectable dependency associated with a DI token. An injector uses the provider 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 application needs.

See also service. See also dependency injection.

Learn more in Dependency Injection.

reactive forms A framework for building Angular forms through code in a component. The alternative is a template-driven form.

When using reactive forms:

The “source of truth”, the form model, is defined in the component class. Validation is set up through validation functions rather than validation directives. Each control is explicitly created in the component class by creating a FormControl instance manually or with FormBuilder. The template input elements do not use ngModel. The associated Angular directives are prefixed with form, such as formControl, formGroup, and formControlName. The alternative is a template-driven form. For an introduction and comparison of both forms approaches, see Introduction to Angular Forms.

resolver A class that implements the Resolve interface that you use to produce or retrieve data that is needed before navigation to a requested route can be completed. You may use a function with the same signature as the resolve() method in place of the Resolve interface. Resolvers run after all route guards for a route tree have been executed and have succeeded.

See an example of using a resolve guard to retrieve dynamic data.

route guard A method that controls navigation to a requested route in a routing application. Guards determine whether a route can be activated or deactivated, and whether a lazy-loaded module can be loaded.

Learn more in the Routing and Navigation guide.

router A tool that configures and implements navigation among states and views within an Angular application.

The Router module is an NgModule that provides the necessary service providers and directives for navigating through application views. A 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.

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 in your Angular applications.

To learn more, see Routing and Navigation.

router outlet A directive that acts as a placeholder in the template of a routing component. Angular dynamically renders the template based on the current router state.

routing component An Angular component with a RouterOutlet directive in its template that displays views based on router navigations.

To learn more, see Routing and Navigation.

rule In schematics, a function that operates on a file tree to create, delete, or modify files in a specific manner.

schematic A scaffolding library that defines how to generate or transform a programming project by creating, modifying, refactoring, or moving files and code. A schematic defines rules that operate on a virtual file system referenced as a tree.

The Angular CLI uses schematics to generate and modify Angular projects and parts of projects.

Angular provides a set of schematics for use with the Angular CLI. See the Angular CLI command reference. The ng add Angular CLI command runs schematics as part of adding a library to your project. The ng generate Angular CLI command runs schematics to create applications, libraries, and Angular code constructs.

Library developers can create schematics that enable the Angular CLI to add and update their published libraries, and to generate artifacts the library defines. Add these schematics to the npm package that you use to publish and share your library.

To learn more, see Schematics. To learn more, see also Integrating Libraries with the CLI.

Schematics CLI Schematics come with their own command-line tool. Use Node 6.9 or above to install the Schematics CLI globally.

content_copy npm install -g @angular-devkit/schematics-cli This installs the schematics executable, which you can use to create a new schematics collection with an initial named schematic. The collection directory is a workspace for schematics. You can also use the schematics command to add a new schematic to an existing collection, or extend an existing schematic.

scoped package 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/forms, and @angular/router.

Import a scoped package in the same way that you import a normal package.

architecture/src/app/app.component.ts (import) content_copy import { Component } from '@angular/core'; server-side rendering A technique that generates static application pages on the server, and can generate and serve those pages in response to requests from browsers. It can also pre-generate pages as HTML files that you serve later.

This technique can improve performance on mobile and low-powered devices and improve the user experience by showing a static first page quickly while the client-side application is loading. The static version can also make your application more visible to web crawlers.

You can easily prepare an application for server-side rendering by using the Angular CLI to run the Angular Universal tool, using the @nguniversal/express-engine schematic.

service In Angular, a class with the @Injectable() decorator that encapsulates non-UI logic and code that can be reused across an application. Angular distinguishes components from services to increase modularity and reusability.

The @Injectable() metadata allows the service class to be used with the dependency injection mechanism. The injectable class is instantiated by a provider. Injectors maintain lists of providers and use them to provide service instances when they are required by components or other services.

To learn more, see Introduction to Services and Dependency Injection.

standalone A configuration of components, directives, and pipes to indicate that this class can be imported directly without declaring it in any NgModule.

Standalone components, directives, and pipes differ from non-standalone ones by:

having the standalone field of their decorator set to true. allowing their direct importing without the need to pass through NgModules. specifying their dependencies directly in their decorator. To learn more, see the Standalone components guide.

structural directive A category of directive that is responsible for shaping HTML layout by modifying the DOM. Modification of the DOM includes, adding, removing, or manipulating elements and the associated children.

To learn more, see Structural Directives.

subscriber A function that defines how to obtain or generate values or messages to be published. This function is executed when a consumer runs the subscribe() method of an 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 an observer JavaScript object 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, or an object. The error notification sends a JavaScript Error or exception. The complete notification does not send a value, but the handler is run when the method completes. Scheduled values can continue to be returned after the method completes. target A buildable or runnable subset of a project, configured as an object in the workspace configuration file, and executed by an Architect builder.

In the angular.json file, each project has an “architect” section that contains targets which configure builders. Some of these targets correspond to Angular CLI command, such as build, serve, test, and lint.

For example, the Architect builder invoked by the ng build command to compile a project uses a particular build tool, and has a default configuration with values that you can override on the command line. The build target also defines an alternate configuration for a “development” build, which you can invoke with the –configuration development flag on the build command.

The Architect tool provides a set of builders. The ng new Angular CLI command provides a set of targets for the initial application project. The ng generate application and ng generate library Angular CLI commands provide a set of targets for each new project. These targets, their options and configurations, can be customized to meet the needs of your project. For example, you may want to add a “staging” or “testing” configuration to the “build” target of a project.

You can also define a custom builder, and add a target to the project configuration that uses your custom builder. You can then run the target using the ng run Angular CLI command.

template Code that defines how to render the view of a component.

A template combines straight HTML with Angular data-binding syntax, directives, and template expressions (logical constructs). The Angular elements insert or calculate values that modify the HTML elements before the page is displayed. Learn more about Angular template language in the Template Syntax guide.

A template is associated with a component class through the @Component() decorator. The template code 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 TemplateRef objects, can define alternative or embedded views, which can be referenced from multiple components.

template-driven forms A format for building Angular forms using HTML forms and input elements in the view. The alternative format uses the reactive forms framework.

When using template-driven forms:

The “source of truth” is the template. The validation is defined using attributes on the individual input elements.

Two-way binding with ngModel keeps the component model synchronized with the user's entry into the input elements.

Behind the scenes, Angular creates a new control for each input element, provided you have set up a name attribute and two-way binding for each input.

The associated Angular directives are prefixed with ng such as ngForm, ngModel, and ngModelGroup.

The alternative is a reactive form. For an introduction and comparison of both forms approaches, see Introduction to Angular Forms.

template expression A TypeScript-like syntax that Angular evaluates within a data binding.

template reference variable A variable defined in a template that references an instance associated with an element, such as a directive instance, component instance, template as in TemplateRef, or DOM element. After declaring a template reference variable on an element in a template, you can access values from that variable elsewhere within the same template. The following example defines a template reference variable named #phone.

src/app/app.component.html content_copy <input #phone placeholder=“phone number” /> To learn more, see Template reference variable.

template input variable A template input variable is a variable you can reference within a single instance of the template. You declare a template input variable using the let keyword as in let customer.

content_copy <tr *ngFor=“let customer of customers;”>

   {{customer.customerNo}}
   {{customer.name}}
   {{customer.address}}
   {{customer.city}}
   {{customer.state}}
   Select

token An opaque identifier used for efficient table lookup. In Angular, a DI token is used to find providers of dependencies in the dependency injection system.

transpile The translation process that transforms one version of JavaScript to another version; for example, down-leveling ES2015 to the older ES5 version.

tree In schematics, a virtual file system represented by the Tree class. Schematic rules take a tree object as input, operate on them, and return a new tree object.

TypeScript A programming language based on JavaScript that is notable for its optional typing system. TypeScript provides compile-time type checking and strong tooling support The type checking and tooling support include 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. To learn more about TypeScript, see typescriptlang.org.

TypeScript configuration file A file specifies the root files and the compiler options required to compile a TypeScript project. To learn more, see TypeScript configuration.

• Angular unidirectional data flow - A data flow model where the component tree is always checked for changes in one direction from parent to child, which prevents cycles in the change detection graph.

In practice, this means that data in Angular flows downward during change detection. A parent component can easily change values in its child components because the parent is checked first. A failure could occur, however, if a child component tries to change a value in its parent during change detection (inverting the expected data flow), because the parent component has already been rendered. In development mode, Angular throws the ExpressionChangedAfterItHasBeenCheckedError error if your application attempts to do this, rather than silently failing to render the new value.

To avoid this error, a lifecycle hook method that seeks to make such a change should trigger a new change detection run. The new run follows the same direction as before, but succeeds in picking up the new value.

• Angular Universal - A tool for implementing server-side rendering of an Angular application. When integrated with an app, Universal generates and serves static pages on the server in response to requests from browsers. The initial static page serves as a fast-loading placeholder while the full application is being prepared for normal execution in the browser. To learn more, see Angular Universal: server-side rendering.

• Angular view - 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.

A component class and its associated template define a view. A view is specifically represented by a ViewRef instance associated with a component. A view that belongs immediately to a component is referenced as a host view. Views are typically collected into view hierarchies.

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.

• Angular View Engine - “A previous compilation and rendering pipeline used by Angular. It has since been replaced by Ivy and is no longer in use. View Engine was deprecated in version 9 and removed in version 13.”

• Angular view hierarchy - “A tree of related views that can be acted on as a unit. The root view referenced as the host view of a component. A host view is the root of a tree of embedded views, collected in a ViewContainerRef view container 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.

• Angular web component - See Angular custom element.

• Angular workspace - “A collection of Angular projects (that is, applications and libraries) powered by the Angular CLI that are typically co-located in a single source-control repository (such as git).”

“The ng new Angular CLI command creates a file system directory (the “workspace root”). In the workspace root, it also creates the workspace configuration file (angular.json) and, by default, an initial application project with the same name.”

Commands that create or operate on applications and libraries (such as add and generate) must be executed from within a workspace directory. To learn more, see Workspace Configuration.

• Angular workspace configuration - “A file named angular.json at the root level of an Angular workspace provides workspace-wide and project-specific Angular configuration defaults for build and development tools that are provided by or integrated with the Angular CLI. To learn more, see Angular Workspace Configuration.

Additional project-specific configuration files are used by tools, such as package.json for the npm package manager, tsconfig.json for TypeScript transpilation, and tslint.json for TSLint. To learn more, see Workspace and Project File Structure.

• Angular zone - “An execution context for a set of asynchronous tasks. Useful for debugging, profiling, and testing applications that include asynchronous operations such as event processing, promises, and runs to remote servers.”

An Angular application 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.

A zone client can take action before and after an async operation completes.

Learn more about zones in this Brian Ford video.

Last reviewed on Mon Feb 28 2022

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