This is the best compilation mode for production environments, with decreased load time and increased performance compared to [just-in-time (JIT) compilation](guide/glossary#jit).
By compiling your application using the `ngc` command-line tool, you can bootstrap directly to a module factory, so you don't need to include the Angular compiler in your JavaScript bundle.
In Angular, an app's root NgModule (`AppModule`) has a `bootstrap` property that identifies the app's top-level [components](guide/glossary#component).
Angular uses capitalization conventions to distinguish the names of various types, as described in the [naming guidelines section](guide/styleguide#02-01) of the Style Guide. Here's a summary of the case types:
A [decorator](guide/glossary#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.
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`.
{@a collection}
## collection
In Angular, a set of related [schematics](#schematic) collected in an [npm package](#npm-package).
The [Angular CLI](cli) is a command-line tool for managing the Angular development cycle. Use it to create the initial filesystem scaffolding for a [workspace](guide/glossary#workspace) or [project](guide/glossary#project), and to run [schematics](guide/glossary#schematic) that add and modify code for initial generic versions of various elements. The CLI supports all stages of the development cycle, including building, testing, bundling, and deployment.
A class with the `@Component()` [decorator](guide/glossary#decorator) that associates it with a companion [template](guide/glossary#template). Together, the component and template define a [view](guide/glossary#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).
A web platform feature, currently supported by most browsers and available in other browsers through polyfills (see [Browser support](guide/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 (also called a *web component*) is recognized by a browser when it's added to the [CustomElementRegistry](https://developer.mozilla.org/en-US/docs/Web/API/CustomElementRegistry).
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 app. The custom element tag inserts the component's view, with change-detection and data-binding functionality, into content that would otherwise be displayed without Angular processing.
A function that modifies a class or property definition. Decorators (also called *annotations*) are an experimental (stage 2) [JavaScript language feature](https://github.com/wycats/javascript-decorators).
A design pattern and mechanism for creating and delivering some parts of an application (dependencies) to other parts of an application that require them.
An [injector](guide/glossary#injector) for an app (created automatically during bootstrap) instantiates dependencies when needed, using a configured [provider](guide/glossary#provider) of the service or value.
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](guide/glossary#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](guide/glossary#template), it creates the matching directive class instance and gives the instance control over that portion of the browser DOM.
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.
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 technique for adding a component to the DOM at run time. Requires that you exclude the component from compilation and then connect it to Angular's change-detection and event-handling framework when you add it to the DOM.
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.
A 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](guide/forms-overview).
{@a form-model}
## 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](guide/glossary#reactive-forms), the form model is created explicitly in the component class. When using [template-driven forms](guide/glossary#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](guide/forms-overview).
{@a form-validation}
## 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](guide/form-validation#adding-to-reactive-forms). Template-driven forms use [validator directives](guide/form-validation#adding-to-template-driven-forms).
To learn more, see [Form Validation](guide/form-validation).
The ability to alter the state of a value after its creation. [Reactive forms](guide/glossary#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](guide/glossary#template-driven-forms) perform mutable changes with `NgModel` and [two-way data binding](guide/glossary#data-binding) to modify the existing data model in place.
An Angular class or other definition that provides a dependency using the [dependency injection](guide/glossary#di) mechanism. An injectable [service](guide/glossary#service) class must be marked by the `@Injectable()` [decorator](guide/glossary#decorator). Other items, such as constant values, can also be injectable.
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.
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.
JIT compilation is the default (as opposed to AOT compilation) 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
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—as opposed to [eager-loaded](guide/glossary#eager-loading) modules that are required by the root module and are thus loaded on launch.
* Library developers can use the [Angular CLI](guide/glossary#cli) to `generate` scaffolding for a new library in an existing [workspace](guide/glossary#workspace), and can publish a library as an `npm` package.
* Application developers can use the [Angular CLI](guide/glossary#cli) to `add` a published library for use with an application in the same [workspace](guide/glossary#workspace).
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.
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 ships as a collection of JavaScript modules (also called libraries). Each Angular library name begins with the `@angular` prefix. Install Angular libraries with the [npm package manager](https://docs.npmjs.com/getting-started/what-is-npm) and import parts of them with JavaScript `import` declarations.
A class definition preceded by the `@NgModule()` [decorator](guide/glossary#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](guide/glossary#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](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`.
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 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 notification of either normal completion or error completion.
An object passed to the `subscribe()` method for an [observable](guide/glossary#observable). The object defines the callbacks for the [subscriber](guide/glossary#subscriber).
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](guide/glossary#view). Angular defines various pipes, and you can define new pipes.
An object that implements one of the [`Provider`](api/core/Provider) interfaces. A provider object defines how to obtain an injectable dependency associated with a [DI token](guide/glossary#token).
An [injector](guide/glossary#injector) uses the provider to create a new instance of a dependency
The alternative is a template-driven form. For an introduction and comparison of both forms approaches, see [Introduction to Angular Forms](guide/forms-overview).
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.
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 [directive](guide/glossary#directive) that acts as a placeholder in a routing component's template. Angular dynamically renders the template based on the current router state.
In [schematics](#schematic), a function that operates on a [file tree](#file-tree) to create, delete, or modify files in a specific manner, and returns a new `Tree` object.
* Angular provides a set of schematics for use with the CLI. See the [Angular CLI command reference](cli). The [`ng add`](cli/add) command runs schematics as part of adding a library to your project. The [`ng generate`](cli/generate) command runs schematics to create apps, libraries, and Angular code constructs.
* [Library](#library) developers can use the [Schematics CLI](#schematics-cli) to create schematics that enable the Angular CLI to add and update their published libraries, and to generate artifacts the library defines.
For more information, see [devkit documentation](https://www.npmjs.com/package/@angular-devkit/schematics).
{@a schematics-cli}
## Schematics CLI
Schematics come with their own command-line tool.
Using Node 6.9 or above, install the Schematics CLI globally:
<code-exampleformat="."language="bash">
npm install -g @angular-devkit/schematics-cli
</code-example>
This installs the `schematics` executable, which you can use to create a new project, add a new schematic to an existing project, or extend an existing schematic.
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`.
In Angular, a class with the [@Injectable()](guide/glossary#injectable) decorator that encapsulates non-UI logic and code that can be reused across an application.
[Injectors](guide/glossary#injector) maintain lists of providers and use them to provide service instances when they are required by components or other services.
A category of [directive](guide/glossary#directive) that is responsible for shaping HTML layout by modifying the DOM&mdashthat is, adding, removing, or manipulating elements and their children.
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](guide/glossary#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, or an object.
* The `error` notification sends a JavaScript Error or exception.
* The `complete` notification doesn't send a value, but the handler is called when the call completes. Scheduled values can continue to be returned after the call completes.
A template is associated with a [component](guide/glossary#component) class through the `@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 `TemplateRef` objects, can define alternative or *embedded* views, which can be referenced from multiple components.
* The "source of truth" is the template. The validation is defined using attributes on the individual input elements.
* [Two-way binding](guide/glossary#data-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 alternative is a reactive form. For an introduction and comparison of both forms approaches, see [Introduction to Angular Forms](guide/forms-overview).
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.
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 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 doesn't 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.
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.
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).
