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1Scan for outdated or missing drivers - takes under a minute2Repair Windows errors before they cause bigger problems3Fix the driver behind crashes, sound loss and screen glitchesAngular applications are assembled as trees of components. To compose one component inside another, make the child available to the parent and place its selector in the parent’s template. Use content projection when callers should supply markup, dependency injection when components need shared services or scoped values, and host directives when a component should acquire reusable host behavior.
How Angular components fit together
A component combines a TypeScript class, an HTML template, and a selector, with configuration supplied through the @Component decorator. The template controls the rendered DOM, the selector identifies how the component is used, and the class supplies behavior. Angular describes components as “the fundamental building block for creating applications in Angular.” Angular Components essentials presents an application as a tree of these building blocks.
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When Angular finds a child component’s selector in a parent template, it creates an instance and renders the child’s view inside the matching host element. This is the basic answer to Angular’s tutorial question, “How do you use a component in your application?” The Angular tutorial demonstrates the idea through hands-on steps.
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One free scan finds every outdated or missing driver and matches the right update for your exact hardware.Free scan · exact hardware matchCompose a child component in a parent template
In current Angular, components are standalone by default. A parent can make a child available by listing it in the parent component’s imports array, then use the child’s selector as an element in its template:
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import { Component } from '@angular/core';
import { ProfilePhoto } from './profile-photo';
@Component({
selector: 'user-profile',
imports: [ProfilePhoto],
template: `
<h1>User profile</h1>
<profile-photo />
`,
})
export class UserProfile {}The child’s selector and its availability in the parent’s compilation context are both necessary: importing the class alone does not render it, and writing the selector does not by itself make the component available. The component guide marks Angular 19 as the default-change boundary: before Angular 19, standalone defaulted to false, so such components are used through the NgModule that declares them. Check the documentation for the Angular release used by your project. Angular’s component guide covers component anatomy and the version distinction.
Keep the child’s public surface explicit. Inputs let a parent provide data, and outputs let it respond to events; these are component APIs, not a reason to route every interaction through a service. The Component API reference documents inputs, outputs, aliases, and template imports.
Choose the composition mechanism that matches the need
| Need | Mechanism | Use it for |
|---|---|---|
| Render a reusable UI unit | Child component selector and imports | A component with its own template and a clear input/output surface. |
| Let the caller supply markup | <ng-content> content projection |
Wrappers such as cards that decide where caller-provided children appear. |
| Share services or scope dependencies | Dependency injection and providers | Reusable behavior or values supplied to components in an injector hierarchy. |
| Add reusable behavior to a component host | hostDirectives |
Compile-time application of directive behavior, with selected inputs and outputs exposed deliberately. |
Use content projection for caller-provided markup
A wrapper component can define one or more <ng-content> placeholders. Angular renders children placed between the wrapper’s opening and closing tags at those placeholder locations. Multiple placeholders can route content by CSS selector. The placeholder is a compile-time instruction, not an ordinary component or DOM element. See Angular’s content projection guide.
Projected children still belong to the parent’s view, even though they appear inside the receiving component. Angular checks them with the parent, and they receive dependencies from the parent’s injector rather than the receiving component’s viewProviders. Consequently, OnPush on the wrapper does not suppress checks for projected content.
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- Do not conditionally include
<ng-content>as a way to avoid creating projected children: Angular instantiates that content even when the placeholder is hidden. - Check a library component’s guidance before supplying children through projection. Controls that manage child keyboard navigation, focus, or ARIA behavior may not reliably support externally projected children.
Use dependency injection for shared services and scoped values
Dependency injection supplies a class with values or services it needs instead of making that class construct them itself. A component can inject a reusable service, while providers can be scoped to a component and its descendants. Angular looks for a requested dependency in the requesting component’s injector and walks upward through the injector hierarchy until it finds a provider. This hierarchy follows the component tree, allowing scoped instances and child overrides. Angular’s dependency injection guide explains the model, and the hierarchical dependency injection guide covers provider resolution.
Injection complements template composition; it does not render a component or replace its inputs and outputs. Use a child component to express a UI relationship, and a service when a class needs a reusable dependency or appropriately scoped shared value.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Use host directives to compose behavior
The directive composition API applies directives to a component’s host through hostDirectives. Angular applies them statically at compile time, so this is not a way to add directives dynamically at runtime. A host directive’s inputs and outputs are not exposed automatically; list and, if useful, alias them explicitly to make them part of the component’s public API. Angular’s directive composition API guide describes the configuration.
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