The <ng-container> allows us to use structural directives without any extra element, making sure that the only DOM changes being applied are those dictated by the directives themselves.
This not only increases performance (even so slightly) since the browser ends up rendering less elements but can also be a valuable asset in having cleaner DOMs and styles alike.
It can for example enable us to use structural directives without breaking styling dependent on a precise DOM structure (as for example the ones we get when using flex containers, margins, the child combinator selector, etc.).
One common use case of <ng-container> is alongside the *ngIf structural directive. By using the special element we can produce very clean templates easy to understand and work with.
For example, we may want to have a number of elements shown conditionally but they do not need to be all under the same root element. That can be easily done by wrapping them in such a block:
Multiple structural directives cannot be used on the same element; if you need to take advantage of more than one structural directive, it is advised to use an <ng-container> per structural directive.
The most common scenario is with *ngIf and *ngFor. For example, let's imagine that we have a list of items but each item needs to be displayed only if a certain condition is true. We could be tempted to try something like:
<ul><li *ngFor="let item of items" *ngIf="item.isValid">
{{ item.name }}
</li></ul>
As we said that would not work, what we can do is to simply move one of the structural directives to an <ng-container> element, which would then wrap the other one, like so:
<ul><ng-container *ngFor="let item of items"><li *ngIf="item.isValid">
{{ item.name }}
</li></ng-container></ul>
This would work as intended without introducing any new unnecessary elements in the DOM.
The NgTemplateOutlet directive can be applied to any element but most of the time it's applied to <ng-container> ones. By combining the two, we get a very clear and easy to follow HTML and DOM structure in which no extra elements are necessary and template views are instantiated where requested.
For example, imagine a situation in which we have a large HTML, in which a small portion needs to be repeated in different places. A simple solution is to define an <ng-template> containing our repeating HTML and render that where necessary by using <ng-container> alongside an NgTemplateOutlet.
With <ng-template>, you can define template content that is only being rendered by Angular when you, whether directly or indirectly, specifically instruct it to do so, allowing you to have full control over how and when the content is displayed.
Note that if you wrap content inside an <ng-template> without instructing Angular to render it, such content will not appear on a page. For example, see the following HTML code, when handling it Angular won't render the middle "Hip!" in the phrase "Hip! Hip! Hooray!" because of the surrounding <ng-template>.
One of the main uses for <ng-template> is to hold template content that will be used by Structural directives. Those directives can add and remove copies of the template content based on their own logic.
Inside the <ng-template> tags you can reference variables present in the surrounding outer template.
Additionally, a context object can be associated with <ng-template> elements.
Such an object contains variables that can be accessed from within the template contents via template (let and as) declarations.
The web is used by a wide variety of people, including those who have visual or motor impairments.
A variety of assistive technologies are available that make it much easier for these groups to interact with web-based software applications.
Also, designing an application to be more accessible generally improves the user experience for all users.
For an in-depth introduction to issues and techniques for designing accessible applications, see the Accessibility section of the Google's Web Fundamentals.
This page discusses best practices for designing Angular applications that work well for all users, including those who rely on assistive technologies.
When binding to ARIA attributes in Angular, you must use the attr. prefix. The ARIA specification depends specifically on HTML attributes rather than properties of DOM elements.
<!-- Use attr. when binding to an ARIA attribute --><button [attr.aria-label]="myActionLabel">…</button>
NOTE
This syntax is only necessary for attribute bindings.
Static ARIA attributes require no extra syntax.
<!-- Static ARIA attributes require no extra syntax --><buttonaria-label="Save document">…</button>
By convention, HTML attributes use lowercase names (tabindex), while properties use camelCase names (tabIndex).
See the Binding syntax guide for more background on the difference between attributes and properties.
The Angular Material library, which is maintained by the Angular team, is a suite of reusable UI components that aims to be fully accessible.
The Component Development Kit (CDK) includes the a11y package that provides tools to support various areas of accessibility.
For example:
LiveAnnouncer is used to announce messages for screen-reader users using an aria-live region.
See the W3C documentation for more information on aria-live regions.
The cdkTrapFocus directive traps Tab-key focus within an element.
Use it to create accessible experience for components such as modal dialogs, where focus must be constrained.
Native HTML elements capture several standard interaction patterns that are important to accessibility.
When authoring Angular components, you should re-use these native elements directly when possible, rather than re-implementing well-supported behaviors.
For example, instead of creating a custom element for a new variety of button, create a component that uses an attribute selector with a native <button> element.
This most commonly applies to <button> and <a>, but can be used with many other types of element.
Sometimes using the appropriate native element requires a container element.
For example, the native <input> element cannot have children, so any custom text entry components need to wrap an <input> with extra elements.
By just including <input> in your custom component's template, it's impossible for your component's users to set arbitrary properties and attributes to the <input> element.
Instead, create a container component that uses content projection to include the native control in the component's API.
You can see MatFormField as an example of this pattern.
The following example shows how to make a progress bar accessible by using host binding to control accessibility-related attributes.
The component defines an accessibility-enabled element with both the standard HTML attribute role, and ARIA attributes.
The ARIA attribute aria-valuenow is bound to the user's input.
src/app/progress-bar.component.ts
import{Component,Input}from'@angular/core';/**
* Example progressbar component.
*/@Component({
selector:'app-example-progressbar',template:'<div class="bar" [style.width.%]="value"></div>',
styleUrls:['./progress-bar.component.css'],
host:{// Sets the role for this component to "progressbar"
role:'progressbar',// Sets the minimum and maximum values for the progressbar role.'aria-valuemin':'0','aria-valuemax':'100',// Binding that updates the current value of the progressbar.'[attr.aria-valuenow]':'value',}})exportclassExampleProgressbarComponent{/** Current value of the progressbar. */@Input()value=0;}
In the template, the aria-label attribute ensures that the control is accessible to screen readers.
src/app/app.component.html
<label>
Enter an example progress value
<inputtype="number"min="0"max="100"
[value]="progress" (input)="setProgress($event)"></label><!-- The user of the progressbar sets an aria-label to communicate what the progress means. --><app-example-progressbar [value]="progress"aria-label="Example of a progress bar"></app-example-progressbar>
Tracking and controlling focus in a UI is an important consideration in designing for accessibility.
When using Angular routing, you should decide where page focus goes upon navigation.
To avoid relying solely on visual cues, you need to make sure your routing code updates focus after page navigation.
Use the NavigationEnd event from the Router service to know when to update focus.
The following example shows how to find and focus the main content header in the DOM after navigation.
router.events.pipe(filter(e => e instanceofNavigationEnd)).subscribe(()=>{const mainHeader = document.querySelector('#main-content-header')if(mainHeader){
mainHeader.focus();}});
In a real application, the element that receives focus depends on your specific application structure and layout.
The focused element should put users in a position to immediately move into the main content that has just been routed into view.
You should avoid situations where focus returns to the body element after a route change.
CSS classes applied to active RouterLink elements, such as RouterLinkActive, provide a visual cue to identify the active link.
Unfortunately, a visual cue doesn't help blind or visually impaired users.
Applying the aria-current attribute to the element can help identify the active link.
For more information, see Mozilla Developer Network (MDN) aria-current).
The RouterLinkActive directive provides the ariaCurrentWhenActive input which sets the aria-current to a specified value when the link becomes active.
The following example shows how to apply the active-page class to active links as well as setting their aria-current attribute to "page" when they are active:
Templates are the user-facing part of an Angular application and are written in HTML.
The following table lists some of the key AngularJS template features with their corresponding Angular template syntax.
In AngularJS, an expression in curly braces denotes one-way binding. This binds the value of the element to a property in the controller associated with this template. When using the controller as syntax, the binding is prefixed with the controller alias vm or $ctrl because you have to be specific about the source.
Bindings/interpolation
Your favorite hero is:{{favoriteHero}}
In Angular, a template expression in curly braces still denotes one-way binding. This binds the value of the element to a property of the component. The context of the binding is implied and is always the associated component, so it needs no reference variable. For more information, see the Interpolation guide.
In Angular you use similar syntax with the pipe | character to filter output, but now you call them pipes. Many, but not all, of the built-in filters from AngularJS are built-in pipes in Angular. For more information, see Filters/pipes.
AngularJS provides more than seventy built-in directives for templates.
Many of them are not needed in Angular because of its more capable and expressive binding system.
The following are some of the key AngularJS built-in directives and their equivalents in Angular.
The application startup process is called bootstrapping. Although you can bootstrap an AngularJS application in code, many applications bootstrap declaratively with the ng-app directive, giving it the name of the module (movieHunter) of the application.
Bootstrappingmain.ts
import{platformBrowserDynamic} from '@angular/platform-browser-dynamic';import{AppModule} from './app/app.module';platformBrowserDynamic().bootstrapModule(AppModule).catch(err => console.error(err));
Angular does not have a bootstrap directive. To launch the application in code, explicitly bootstrap the root module (AppModule) of the application in main.ts and the root component (AppComponent) of the application in app.module.ts.
In AngularJS, the ng-class directive includes/excludes CSS classes based on an expression. The expression is often a key-value object, with key defined as a CSS class name, and value as a template expression that evaluates to a Boolean. In the first example, the active class is applied to the element if isActive is true. You can specify multiple classes, as shown in the second example.
In Angular, the ngClass directive works similarly. It includes/excludes CSS classes based on an expression. In the first example, the active class is applied to the element if isActive is true. You can specify multiple classes, as shown in the second example. Angular also has class binding, which is a good way to add or remove a single class, as shown in the third example. For more information see Attribute, class, and style bindings page.
In AngularJS, the ng-click directive allows you to specify custom behavior when an element is clicked. In the first example, when the user clicks the button, the toggleImage() method in the controller referenced by the vmcontroller as alias is executed. The second example demonstrates passing in the $event object, which provides details about the event to the controller.
AngularJS event-based directives do not exist in Angular. Rather, define one-way binding from the template view to the component using event binding. For event binding, define the name of the target event within parenthesis and specify a template statement, in quotes, to the right of the equals. Angular then sets up an event handler for the target event. When the event is raised, the handler executes the template statement. In the first example, when a user clicks the button, the toggleImage() method in the associated component is executed. The second example demonstrates passing in the $event object, which provides details about the event to the component. For a list of DOM events, see Event reference. For more information, see the Event binding page.
In AngularJS, the ng-controller directive attaches a controller to the view. Using the ng-controller, or defining the controller as part of the routing, ties the view to the controller code associated with that view.
In Angular, the template no longer specifies its associated controller. Rather, the component specifies its associated template as part of the component class decorator. For more information, see Architecture Overview.
The ng-href directive allows AngularJS to preprocess the href property. ng-href can replace the binding expression with the appropriate URL before the browser fetches from that URL. In AngularJS, the ng-href is often used to activate a route as part of navigation.
<ang-href="#{{ moviesHash }}">
Movies
</a>
Routing is handled differently in Angular.
Bind to the href property
<a [href]="angularDocsUrl">Angular Docs</a>
Angular uses property binding. Angular does not have a built-in href directive. Place the href property of the element in square brackets and set it to a quoted template expression. For more information see the Property binding page. In Angular, href is no longer used for routing. Routing uses routerLink, as shown in the following example.
In AngularJS, the ng-if directive removes or recreates a section of the DOM, based on an expression. If the expression is false, the element is removed from the DOM. In this example, the <table> element is removed from the DOM unless the movies array has a length greater than zero.
The *ngIf directive in Angular works the same as the ng-if directive in AngularJS. It removes or recreates a section of the DOM based on an expression. In this example, the <table> element is removed from the DOM unless the movies array has a length. The (*) before ngIf is required in this example. For more information, see Structural Directives.
In AngularJS, the ng-model directive binds a form control to a property in the controller associated with the template. This provides two-way binding whereby changes result in the value in the view and the model being synchronized.
In AngularJS, the ng-repeat directive repeats the associated DOM element for each item in the specified collection. In this example, the table row (<tr>) element repeats for each movie object in the collection of movies.
The *ngFor directive in Angular is like the ng-repeat directive in AngularJS. It repeats the associated DOM element for each item in the specified collection. More accurately, it turns the defined element (<tr> in this example) and its contents into a template and uses that template to instantiate a view for each item in the list. Notice the other syntax differences:
<h3ng-show="vm.favoriteHero">
Your favorite hero is: {{vm.favoriteHero}}
</h3>
In AngularJS, the ng-show directive shows or hides the associated DOM element, based on an expression. In this example, the <div> element is shown if the favoriteHero variable is truthy.
Bind to the hidden property
<h3 [hidden]="!favoriteHero">
Your favorite hero is: {{favoriteHero}}
</h3>
Angular uses property binding. Angular has no built-in show directive. For hiding and showing elements, bind to the HTML hidden property. To conditionally display an element the hidden property of the element can be used. Place the hidden property in square brackets and set it to a quoted template expression that evaluates to the opposite of show. In this example, the <div> element is hidden if the favoriteHero variable is not truthy. For more information on property binding, see the Property binding page.
The ng-src directive allows AngularJS to preprocess the src property. This replaces the binding expression with the appropriate URL before the browser fetches from that URL.
Angular uses property binding. Angular has no built-in src directive. Place the src property in square brackets and set it to a quoted template expression. For more information on property binding, see the Property binding page.
In AngularJS, the ng-style directive sets a CSS style on an HTML element based on an expression. That expression is often a key-value control object with:
each key of the object defined as a CSS property
each value defined as an expression that evaluates to a value appropriate for the style
In the example, the color style is set to the current value of the colorPreference variable.
In Angular, the ngStyle directive works similarly. It sets a CSS style on an HTML element based on an expression. In the first example, the color style is set to the current value of the colorPreference variable. Angular also has style binding, which is good way to set a single style. This is shown in the second example. For more information on style binding, see the Style binding section of the Attribute binding page. For more information on the ngStyle directive, see the NgStyle section of the Built-in directives page.
<divng-switch="vm.favoriteHero && vm.checkMovieHero(vm.favoriteHero)"><divng-switch-when="true">
Excellent choice.
</div><divng-switch-when="false">
No movie, sorry.
</div><divng-switch-default>
Please enter your favorite hero.
</div></div>
In AngularJS, the ng-switch directive swaps the contents of an element by selecting one of the templates based on the current value of an expression. In this example, if favoriteHero is not set, the template displays "Please enter …" If favoriteHero is set, it checks the movie hero by calling a controller method. If that method returns true, the template displays "Excellent choice!" If that methods returns false, the template displays "No movie, sorry!"
<span [ngSwitch]="favoriteHero &&
checkMovieHero(favoriteHero)"><p *ngSwitchCase="true">
Excellent choice!
</p><p *ngSwitchCase="false">
No movie, sorry!
</p><p *ngSwitchDefault>
Please enter your favorite hero.
</p></span>
In Angular, the ngSwitch directive works similarly. It displays an element whose *ngSwitchCase matches the current ngSwitch expression value. In this example, if favoriteHero is not set, the ngSwitch value is null and *ngSwitchDefault displays, "Please enter your favorite hero." If favoriteHero is set, the application checks the movie hero by calling a component method. If that method returns true, the application selects *ngSwitchCase="true" and displays: "Excellent choice." If that methods returns false, the application selects *ngSwitchCase="false" and displays: "No movie, sorry." The (*) before ngSwitchCase and ngSwitchDefault is required in this example. For more information, see The NgSwitch directives section of the Built-in directives page.
Angular pipes provide formatting and transformation for data in the template, like AngularJS filters.
Many of the built-in filters in AngularJS have corresponding pipes in Angular.
For more information on pipes, see Pipes.
<trng-repeat="movie in movieList | filter: {title:listFilter}">
Selects a subset of items from the defined collection, based on the filter criteria.
none For performance reasons, no comparable pipe exists in Angular. Do all your filtering in the component. If you need the same filtering code in several templates, consider building a custom pipe.
The SlicePipe does the same thing but the order of the parameters is reversed, in keeping with the JavaScript Slice method. The first parameter is the starting index and the second is the limit. As in AngularJS, coding this operation within the component instead could improve performance.
The Angular number pipe is similar. It provides more capabilities when defining the decimal places, as shown in the preceding second example. Angular also has a percent pipe, which formats a number as a local percentage as shown in the third example.
<trng-repeat="movie in movieList | orderBy : 'title'">
Displays the collection in the order specified by the expression. In this example, the movie title orders the movieList.
none For performance reasons, no comparable pipe exists in Angular. Instead, use component code to order or sort results. If you need the same ordering or sorting code in several templates, consider building a custom pipe.
In both AngularJS and Angular, modules help you organize your application into cohesive blocks of features.
In AngularJS, you write the code that provides the model and the methods for the view in a controller.
In Angular, you build a component.
Because much AngularJS code is in JavaScript, JavaScript code is shown in the AngularJS column.
The Angular code is shown using TypeScript.
Immediately invoked function expression (IIFE) → nonelink
AngularJS
Angular
IIFE
(function(){…}());
In AngularJS, an IIFE around controller code keeps it out of the global namespace.
none This is a nonissue in Angular because ES 2015 modules handle the namespace for you. For more information on modules, see the Modules section of the Architecture Overview.
In AngularJS, an Angular module keeps track of controllers, services, and other code. The second argument defines the list of other modules that this module depends upon.
AngularJS has code in each controller that looks up an appropriate Angular module and registers the controller with that module. The first argument is the controller name. The second argument defines the string names of all dependencies injected into this controller, and a reference to the controller function.
Angular adds a decorator to the component class to provide any required metadata. The @Component decorator declares that the class is a component and provides metadata about that component such as its selector, or tag, and its template. This is how you associate a template with logic, which is defined in the component class. For more information, see the Components section of the Architecture Overview page.
In AngularJS, you write the code for the model and methods in a controller function.
Component class
exportclassMovieListComponent{}
In Angular, you create a component class to contain the data model and control methods. Use the TypeScript export keyword to export the class so that the component can be imported into NgModules. For more information, see the Components section of the Architecture Overview page.
In AngularJS, you pass in any dependencies as controller function arguments. This example injects a MovieService. To guard against minification problems, tell Angular explicitly that it should inject an instance of the MovieService in the first parameter.
Dependency injection
constructor(movieService:MovieService){}
In Angular, you pass in dependencies as arguments to the component class constructor. This example injects a MovieService. The TypeScript type of the first parameter tells Angular what to inject, even after minification. For more information, see the Dependency injection section of the Architecture Overview.
Style sheets give your application a nice look.
In AngularJS, you specify the style sheets for your entire application.
As the application grows over time, the styles for the many parts of the application merge, which can cause unexpected results.
In Angular, you can still define style sheets for your entire application.
Now you can also encapsulate a style sheet within a specific component.
The template options object, angularCompilerOptions, is a sibling to the compilerOptions object that supplies standard options to the TypeScript compiler.
Like the TypeScript compiler, the Angular AOT compiler also supports extends in the angularCompilerOptions section of the TypeScript configuration file.
The extends property is at the top level, parallel to compilerOptions and angularCompilerOptions.
A TypeScript configuration can inherit settings from another file using the extends property.
The configuration options from the base file are loaded first, then overridden by those in the inheriting configuration file.
When true, create all possible files even if they are empty.
Default is false.
Used by the Bazel build rules to simplify how Bazel rules track file dependencies.
Do not use this option outside of the Bazel rules.
Modifies how Angular-specific annotations are emitted to improve tree-shaking.
Non-Angular annotations are not affected.
One of static fields or decorators. The default value is static fields.
By default, the compiler replaces decorators with a static field in the class, which allows advanced tree-shakers like Closure compiler to remove unused classes
The decorators value leaves the decorators in place, which makes compilation faster.
TypeScript emits calls to the __decorate helper.
Use --emitDecoratorMetadata for runtime reflection.
NOTE:
That the resulting code cannot tree-shake properly.
When true, the default, transforms code that is or could be used in an annotation, to allow it to be imported from template factory modules.
See metadata rewriting for more information.
When false, disables this rewriting, requiring the rewriting to be done manually.
When true, the compiler does not look at the TypeScript version and does not report an error when an unsupported version of TypeScript is used.
Not recommended, as unsupported versions of TypeScript might have undefined behavior.
Default is false.
Instructs the Angular template compiler to create legacy ids for messages that are tagged in templates by the i18n attribute.
See Mark text for translations for more information about marking messages for localization.
Set this option to false unless your project relies upon translations that were created earlier using legacy IDs.
Default is true.
The pre-Ivy message extraction tooling created a variety of legacy formats for extracted message IDs.
These message formats have some issues, such as whitespace handling and reliance upon information inside the original HTML of a template.
The new message format is more resilient to whitespace changes, is the same across all translation file formats, and can be created directly from calls to $localize.
This allows $localize messages in application code to use the same ID as identical i18n messages in component templates.
When true, enables the deprecated <template> element in place of <ng-template>.
Default is false.
Might be required by some third-party Angular libraries.
The module ID to use for importing a flat module (when flatModuleOutFile is true).
References created by the template compiler use this module name when importing symbols from the flat module.
Ignored if flatModuleOutFile is false.
When true, generates a flat module index of the given filename and the corresponding flat module metadata.
Use to create flat modules that are packaged similarly to @angular/core and @angular/common.
When this option is used, the package.json for the library should refer to the created flat module index instead of the library index file.
Produces only one .metadata.json file, which contains all the metadata necessary for symbols exported from the library index.
In the created .ngfactory.js files, the flat module index is used to import symbols. Symbols that include both the public API from the library index as well as shrouded internal symbols.
By default the .ts file supplied in the files field is assumed to be the library index.
If more than one .ts file is specified, libraryIndex is used to select the file to use.
If more than one .ts file is supplied without a libraryIndex, an error is produced.
A flat module index .d.ts and .js is created with the given flatModuleOutFile name in the same location as the library index .d.ts file.
For example, if a library uses the public_api.ts file as the library index of the module, the tsconfig.jsonfiles field would be ["public_api.ts"].
The flatModuleOutFile option could then be set, for example, to "index.js", which produces index.d.ts and index.metadata.json files.
The module field of the library's package.json would be "index.js" and the typings field would be "index.d.ts".
When true, the recommended value, enables the binding expression validation phase of the template compiler. This phase uses TypeScript to verify binding expressions.
For more information, see Template type checking.
Default is false, but when you use the Angular CLI command ng new --strict, it is set to true in the new project's configuration.
The fullTemplateTypeCheck option has been deprecated in Angular 13 in favor of the strictTemplates family of compiler options.
When false, the default, removes blank text nodes from compiled templates, which results in smaller emitted template factory modules.
Set to true to preserve blank text nodes.
When true, does not produce .metadata.json files.
Default is false.
The .metadata.json files contain information needed by the template compiler from a .ts file that is not included in the .d.ts file produced by the TypeScript compiler.
This information includes, for example, the content of annotations, such as a component's template, which TypeScript emits to the .js file but not to the .d.ts file.
You can set to true when using factory summaries, because the factory summaries include a copy of the information that is in the .metadata.json file.
Set to true if you are using TypeScript's --outFile option, because the metadata files are not valid for this style of TypeScript output.
The Angular community does not recommend using --outFile with Angular.
Use a bundler, such as webpack, instead.
When true, does not emit .ngfactory.js and .ngstyle.js files.
This turns off most of the template compiler and disables the reporting of template diagnostics.
Can be used to instruct the template compiler to produce .metadata.json files for distribution with an npm package. This avoids the production of .ngfactory.js and .ngstyle.js files that cannot be distributed to npm.
For library projects created with the Angular CLI, the development configuration default is true.
When true, reports an error to the .metadata.json file if "skipMetadataEmit" is false.
Default is false.
Use only when "skipMetadataEmit" is false and "skipTemplateCodegen" is true.
This option is intended to verify the .metadata.json files emitted for bundling with an npm package.
The validation is strict and can emit errors for metadata that would never produce an error when used by the template compiler.
You can choose to suppress the error emitted by this option for an exported symbol by including @dynamic in the comment documenting the symbol.
It is valid for .metadata.json files to contain errors.
The template compiler reports these errors if the metadata is used to determine the contents of an annotation.
The metadata collector cannot predict the symbols that are designed for use in an annotation. It preemptively includes error nodes in the metadata for the exported symbols.
The template compiler can then use the error nodes to report an error if these symbols are used.
If the client of a library intends to use a symbol in an annotation, the template compiler does not normally report this. It gets reported after the client actually uses the symbol.
This option allows detection of these errors during the build phase of the library and is used, for example, in producing Angular libraries themselves.
For library projects created with the Angular CLI, the development configuration default is true.
When true, reports an error for a supplied parameter whose injection type cannot be determined.
When false, constructor parameters of classes marked with @Injectable whose type cannot be resolved produce a warning.
The recommended value is true, but the default value is false.
When you use the Angular CLI command ng new --strict, it is set to true in the created project's configuration.
The strictness flags that this open enables allow you to turn on and off specific types of strict template type checking.
See troubleshooting template errors.
When you use the Angular CLI command ng new --strict, it is set to true in the new project's configuration.
Most of the time you interact with the Angular Compiler indirectly using Angular CLI. When debugging certain issues, you might find it useful to invoke the Angular Compiler directly.
You can use the ngc command provided by the @angular/compiler-cli npm package to call the compiler from the command line.
The ngc command is just a wrapper around TypeScript's tsc compiler command and is primarily configured via the tsconfig.json configuration options documented in the previous sections.
This document describes the Angular Package Format (APF).
APF is an Angular specific specification for the structure and format of npm packages that is used by all first-party Angular packages (@angular/core, @angular/material, etc.) and most third-party Angular libraries.
APF enables a package to work seamlessly under most common scenarios that use Angular.
Packages that use APF are compatible with the tooling offered by the Angular team as well as wider JavaScript ecosystem.
It is recommended that third-party library developers follow the same npm package format.
APF is versioned along with the rest of Angular, and every major version improves the package format.
You can find the versions of the specification prior to v13 in this google doc.
In today's JavaScript landscape, developers consume packages in many different ways, using many different toolchains (Webpack, rollup, esbuild, etc.).
These tools may understand and require different inputs - some tools may be able to process the latest ES language version, while others may benefit from directly consuming an older ES version.
The Angular distribution format supports all of the commonly used development tools and workflows, and adds emphasis on optimizations that result either in smaller application payload size or faster development iteration cycle (build time).
Developers can rely on Angular CLI and ng-packagr (a build tool Angular CLI uses) to produce packages in the Angular package format.
See the Creating Libraries guide for more details.
The following example shows a simplified version of the @angular/core package's file layout, with an explanation for each file in the package.
node_modules/@angular/core
README.md
package.json
index.d.ts
esm2020
core.mjs
index.mjs
public_api.mjs
testing
fesm2015
core.mjs
core.mjs.map
testing.mjs
testing.mjs.map
fesm2020
core.mjs
core.mjs.map
testing.mjs
testing.mjs.map
testing
index.d.ts
This table describes the file layout under node_modules/@angular/core annotated to describe the purpose of files and directories:
Files
Purpose
README.md
Package README, used by npmjs web UI.
package.json
Primary package.json, describing the package itself as well as all available entrypoints and code formats. This file contains the "exports" mapping used by runtimes and tools to perform module resolution.
index.d.ts
Bundled .d.ts for the primary entrypoint @angular/core.
esm2020/ ─ core.mjs ─ index.mjs ─ public_api.mjs
Tree of @angular/core sources in unflattened ES2020 format.
esm2020/testing/
Tree of the @angular/core/testing entrypoint in unflattened ES2020 format.
The primary package.json contains important package metadata, including the following:
It declares the package to be in EcmaScript Module (ESM) format
It contains an "exports" field which defines the available source code formats of all entrypoints
It contains keys which define the available source code formats of the primary @angular/core entrypoint, for tools which do not understand "exports".
These keys are considered deprecated, and could be removed as the support for "exports" rolls out across the ecosystem.
It declares whether the package contains side effects
Of primary interest are the "." and the "./testing" keys, which define the available code formats for the @angular/core primary entrypoint and the @angular/core/testing secondary entrypoint, respectively.
For each entrypoint, the available formats are:
Formats
Details
Typings (.d.ts files)
.d.ts files are used by TypeScript when depending on a given package.
es2020
ES2020 code flattened into a single source file.
es2015
ES2015 code flattened into a single source file.
esm2020
ES2020 code in unflattened source files (this format is included for experimentation - see this discussion of defaults for details).
Tooling that is aware of these keys may preferentially select a desirable code format from "exports".
The remaining 2 keys control the default behavior of tooling:
"node" selects flattened ES2015 code when the package is loaded in Node.
This format is used due to the requirements of zone.js, which does not support native async/await ES2017 syntax.
Therefore, Node is instructed to use ES2015 code, where async/await structures have been downleveled into Promises.
"default" selects flattened ES2020 code for all other consumers.
Libraries may want to expose additional static files which are not captured by the exports of the JavaScript-based entry-points such as Sass mixins or pre-compiled CSS.
In addition to "exports", the top-level package.json also defines legacy module resolution keys for resolvers that don't support "exports".
For @angular/core these are:
As shown in the preceding code snippet, a module resolver can use these keys to load a specific code format.
NOTE:
Instead of "default", "module" selects the format both for Node as well as any tooling not configured to use a specific key.
As with "node", ES2015 code is selected due to the constraints of ZoneJS.
Packages in the Angular Package Format contain one primary entrypoint and zero or more secondary entrypoints (for example, @angular/common/http).
Entrypoints serve several functions.
They define the module specifiers from which users import code (for example, @angular/core and @angular/core/testing).
Users typically perceive these entrypoints as distinct groups of symbols, with different purposes or capability.
Specific entrypoints might only be used for special purposes, such as testing.
Such APIs can be separated out from the primary entrypoint to reduce the chance of them being used accidentally or incorrectly.
They define the granularity at which code can be lazily loaded.
Many modern build tools are only capable of "code splitting" (aka lazy loading) at the ES Module level.
The Angular Package Format uses primarily a single "flat" ES Module per entry point. This means that most build tooling is not able to split code with a single entry point into multiple output chunks.
The general rule for APF packages is to use entrypoints for the smallest sets of logically connected code possible.
For example, the Angular Material package publishes each logical component or set of components as a separate entrypoint - one for Button, one for Tabs, etc.
This allows each Material component to be lazily loaded separately, if desired.
Not all libraries require such granularity.
Most libraries with a single logical purpose should be published as a single entrypoint.
@angular/core for example uses a single entrypoint for the runtime, because the Angular runtime is generally used as a single entity.
The README file in the Markdown format that is used to display description of a package on npm and GitHub.
Example README content of @angular/core package:
Angular
=======
The sources for this package are in the main [Angular](https://github.com/angular/angular) repo.Please file issues and pull requests against that repo.
License: MIT
Libraries in the Angular Package Format must be published in "partial compilation" mode.
This is a compilation mode for ngc which produces compiled Angular code that is not tied to a specific Angular runtime version, in contrast to the full compilation used for applications, where the Angular compiler and runtime versions must match exactly.
To partially compile Angular code, use the compilationMode flag in the angularCompilerOptions property of your tsconfig.json:
The Angular Package Format specifies that code be published in "flattened" ES module format.
This significantly reduces the build time of Angular applications as well as download and parse time of the final application bundle.
Please check out the excellent post "The cost of small modules" by Nolan Lawson.
The Angular compiler can generate index ES module files. Tools like Rollup can use these files to generate flattened modules in a Flattened ES Module (FESM) file format.
FESM is a file format created by flattening all ES Modules accessible from an entrypoint into a single ES Module.
It's formed by following all imports from a package and copying that code into a single file while preserving all public ES exports and removing all private imports.
The abbreviated name, FESM, pronounced phe-som, can be followed by a number such as FESM5 or FESM2015.
The number refers to the language level of the JavaScript inside the module.
Accordingly a FESM5 file would be ESM+ES5 and include import/export statements and ES5 source code.
To generate a flattened ES Module index file, use the following configuration options in your tsconfig.json file:
Once the index file (for example, my-ui-lib.js) is generated by ngc, bundlers and optimizers like Rollup can be used to produce the flattened ESM file.
As of webpack v4, the flattening of ES modules optimization should not be necessary for webpack users. It should be possible to get better code-splitting without flattening of modules in webpack.
In practice, size regressions can still be seen when using unflattened modules as input for webpack v4.
This is why module and es2020 package.json entries still point to FESM files.
This issue is being investigated. It is expected to switch the module and es2020 package.json entry points to unflattened files after the size regression issue is resolved.
The APF currently includes unflattened ESM2020 code for the purpose of validating such a future change.
By default, EcmaScript Modules are side-effectful: importing from a module ensures that any code at the top level of that module should run.
This is often undesirable, as most side-effectful code in typical modules is not truly side-effectful, but instead only affects specific symbols.
If those symbols are not imported and used, it's often desirable to remove them in an optimization process known as tree-shaking, and the side-effectful code can prevent this.
Build tools such as Webpack support a flag which allows packages to declare that they do not depend on side-effectful code at the top level of their modules, giving the tools more freedom to tree-shake code from the package.
The end result of these optimizations should be smaller bundle size and better code distribution in bundle chunks after code-splitting.
This optimization can break your code if it contains non-local side-effects - this is however not common in Angular applications and it's usually a sign of bad design.
The recommendation is for all packages to claim the side-effect free status by setting the sideEffects property to false, and that developers follow the Angular Style Guide which naturally results in code without non-local side-effects.
ES2020 Language level is now the default language level that is consumed by Angular CLI and other tooling.
The Angular CLI down-levels the bundle to a language level that is supported by all targeted browsers at application build time.
As of APF v8 it is now preferred to run API Extractor, to bundle TypeScript definitions so that the entire API appears in a single file.
In prior APF versions each entry point would have a src directory next to the .d.ts entry point and this directory contained individual d.ts files matching the structure of the original source code.
While this distribution format is still allowed and supported, it is highly discouraged because it confuses tools like IDEs that then offer incorrect autocompletion, and allows users to depend on deep-import paths which are typically not considered to be public API of a library or a package.
As of APF v10, it is recommended to add tslib as a direct dependency of your primary entry-point.
This is because the tslib version is tied to the TypeScript version used to compile your library.
The smallest set of files that are published to NPM and installed together, for example @angular/core.
This package includes a manifest called package.json, compiled source code, typescript definition files, source maps, metadata, etc.
The package is installed with npm install @angular/core.
Short for ECMAScript Modules.
A file containing statements that import and export symbols.
This is identical to the definition of modules in the ECMAScript spec.
Short for Flattened ES Modules and consists of a file format created by flattening all ES Modules accessible from an entry point into a single ES Module.
The identifier of a module used in the import statements (for example, @angular/core).
The ID often maps directly to a path on the filesystem, but this is not always the case due to various module resolution strategies.
Algorithm used to convert Module IDs to paths on the filesystem.
Node.js has one that is well specified and widely used, TypeScript supports several module resolution strategies, Closure Compiler has yet another strategy.
Specification of the module syntax that covers at minimum the syntax for the importing and exporting from a file.
Common module formats are CommonJS (CJS, typically used for Node.js applications) or ECMAScript Modules (ESM).
The module format indicates only the packaging of the individual modules, but not the JavaScript language features used to make up the module content.
Because of this, the Angular team often uses the language level specifier as a suffix to the module format, (for example, ESM+ES2015 specifies that the module is in ESM format and contains code down-leveled to ES2015).
An artifact in the form of a single JS file, produced by a build tool (for example, Webpack or Rollup) that contains symbols originating in one or more modules.
Bundles are a browser-specific workaround that reduce network strain that would be caused if browsers were to start downloading hundreds if not tens of thousands of files.
Node.js typically doesn't use bundles.
Common bundle formats are UMD and System.register.
A module intended to be imported by the user.
It is referenced by a unique module ID and exports the public API referenced by that module ID.
An example is @angular/core or @angular/core/testing.
Both entry points exist in the @angular/core package, but they export different symbols.
A package can have many entry points.
A process of retrieving symbols from modules that are not Entry Points.
These module IDs are usually considered to be private APIs that can change over the lifetime of the project or while the bundle for the given package is being created.
An import coming from an entry point.
The available top-level imports are what define the public API and are exposed in "@angular/name" modules, such as @angular/core or @angular/common.
The process of identifying and removing code not used by an application - also known as dead code elimination.
This is a global optimization performed at the application level using tools like Rollup, Closure Compiler, or Terser.
You can define a set of styles together to make up a specific state for animating elements and transitions. These states represent style at certain points in your animations that you can animate to and from. For example, you can animate a state as the starting point to a different state and the end of an animation.
A state is the condition of an animation. The Angular state() function takes two parameters: a unique name and a style. There is also an optional parameter.
Aliasing a set of styles and allows you to reference that alias for animations in general. This can make animations more readable or more understandable at a glance. You can give animations a useful and descriptive state name, which allows you to quickly understand the purpose of that animation state.
Use Angular's state() function to define different states to call at the end of each transition.
This function takes two arguments:
A unique name like open or closed and a style() function.
Use the style() function to define a set of styles to associate with a given state name.
You must use camelCase for style attributes that contain dashes, such as backgroundColor or wrap them in quotes, such as 'background-color'.
Angular's state() function works with the style() function to set CSS style attributes.
In this code snippet, multiple style attributes are set at the same time for the state.
In the open state, the button has a height of 200 pixels, an opacity of 1, and a yellow background color.
The functional API provided by the @angular/animations module provides a domain-specific language (DSL) for creating and controlling animations in Angular applications.
See the API reference for a complete listing and syntax details of the core functions and related data structures.
Kicks off the animation and serves as a container for all other animation function calls. HTML template binds to triggerName. Use the first argument to declare a unique trigger name. Uses array syntax.
Creates a named set of CSS styles that should be applied on successful transition to a given state. The state can then be referenced by name within other animation functions.
Allows a sequential change between styles within a specified time interval. Use within animate(). Can include multiple style() calls within each keyframe(). Uses array syntax.
Specifies a group of animation steps (inner animations) to be run in parallel. Animation continues only after all inner animation steps have completed. Used within sequence() or transition().
An animation transition specifies changes that occur between one state and another. Set the transition to make the change less abrupt. An animation transition specifies the changes that occur between one state and another.
An expression that defines the direction between two transition states
An expression that accepts one or a series of animate() steps
Use the animate() function of a transition to define:
Length
Delay
Easing
Style function for defining styles while transitions are taking place
Use the animate() function to define the keyframes() function for multi-step animations.
These definitions are placed in the second argument of the animate() function.
Animation metadata: duration, delay, and easinglink
The animate() function accepts the timings and styles input parameters.
The timings parameter takes either a number or a string defined in three parts.
The first part, duration, is required.
The duration can be expressed in milliseconds as a number without quotes, or in seconds with quotes and a time specifier.
For example, a duration of a tenth of a second can be expressed as follows:
As a plain number, in milliseconds:
100
In a string, as milliseconds:
'100ms'
In a string, as seconds:
'0.1s'
The second argument, delay, has the same syntax as duration.
For example:
Wait for 100 ms and then run for 200 ms: '0.2s 100ms'
The third argument, easing, controls how the animation accelerates and decelerates during its runtime.
For example, ease-in causes the animation to begin slowly, and to pick up speed as it progresses.
Wait for 100 ms, run for 200 ms.
Use a deceleration curve to start out fast and slowly decelerate to a resting point:
0.2s100ms ease-out
Run for 200 ms, with no delay.
Use a standard curve to start slow, speed up in the middle, and then decelerate slowly at the end:
0.2s ease-in-out
Start immediately, run for 200 ms.
Use an acceleration curve to start slow and end at full velocity:
The code sample is missing.
0.2s ease-in
NOTE:
See the Material Design website's topic on Natural easing curves for general information on easing curves.
This example provides a state transition from open to closed with a 1-second transition between states.
In the preceding code snippet, the => operator indicates unidirectional transitions, and <=> is bidirectional.
Within the transition, animate() specifies how long the transition takes.
In this case, the state change from open to closed takes 1 second, expressed here as 1s.
This example adds a state transition from the closed state to the open state with a 0.5-second transition animation arc.
