183 lines
7.0 KiB
Markdown
183 lines
7.0 KiB
Markdown
# Angular Components Overview
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Components are the main building block for Angular applications. Each component consists of:
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* An HTML template that declares what renders on the page
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* A Typescript class that defines behavior
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* A CSS selector that defines how the component is used in a template
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* Optionally, CSS styles applied to the template
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This topic describes how to create and configure an Angular component.
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<div class="alert is-helpful">
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To view or download the example code used in this topic, see the <live-example></live-example>.
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</div>
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## Prerequisites
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To create a component, verify that you have met the following prerequisites:
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1. Install the Angular CLI.
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1. Create an Angular project.
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If you don't have a project, you can create one using `ng new <project-name>`, where `<project-name>` is the name of your Angular application.
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## Creating a component
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The easiest way to create a component is with the Angular CLI. You can also create a component manually.
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### Creating a component using the Angular CLI
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To create a component using the Angular CLI:
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1. From a terminal window, navigate to the directory containing your application.
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1. Run the `ng generate component <component-name>` command, where `<component-name>` is the name of your new component.
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By default, this command creates the following:
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* A folder named after the component
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* A component file, `<component-name>.component.ts`
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* A template file, `<component-name>.component.html`
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* A CSS file, `<component-name>.component.css`
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* A testing specification file, `<component-name>.component.spec.ts`
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Where `<component-name>` is the name of your component.
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<div class="alert is-helpful">
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You can change how `ng generate component` creates new components.
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For more information, see [ng generate component](cli/generate#component-command) in the Angular CLI documentation.
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</div>
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### Creating a component manually
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Although the Angular CLI is the easiest way to create an Angular component, you can also create a component manually.
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This section describes how to create the core component file within an existing Angular project.
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To create a new component manually:
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1. Navigate to your Angular project directory.
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1. Create a new file, `<component-name>.component.ts`.
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1. At the top of the file, add the following import statement.
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<code-example
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path="component-overview/src/app/component-overview/component-overview.component.ts"
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region="import">
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</code-example>
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1. After the `import` statement, add a `@Component` decorator.
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<code-example
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path="component-overview/src/app/component-overview/component-overview.component.ts"
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region="decorator-skeleton">
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</code-example>
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1. Choose a CSS selector for the component.
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<code-example
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path="component-overview/src/app/component-overview/component-overview.component.ts"
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region="selector">
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</code-example>
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For more information on choosing a selector, see [Specifying a component's selector](#specifying-a-components-css-selector).
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1. Define the HTML template that the component uses to display information.
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In most cases, this template is a separate HTML file.
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<code-example
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path="component-overview/src/app/component-overview/component-overview.component.ts"
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region="templateUrl">
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</code-example>
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For more information on defining a component's template, see [Defining a component's template](#defining-a-components-template).
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1. Select the styles for the component's template.
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In most cases, you define the styles for your component's template in a separate file.
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<code-example
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path="component-overview/src/app/component-overview/component-overview.component.ts"
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region="decorator">
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</code-example>
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1. Add a `class` statement that includes the code for the component.
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<code-example
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path="component-overview/src/app/component-overview/component-overview.component.ts"
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region="class">
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</code-example>
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## Specifying a component's CSS selector
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Every component requires a CSS _selector_. A selector instructs Angular to instantiate this component wherever it finds the corresponding tag in template HTML. For example, consider a component `hello-world.component.ts` that defines its selector as `app-hello-world`. This selector instructs Angular to instantiate this component any time the tag `<app-hello-world>` appears in a template.
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Specify a component's selector by adding a `selector` statement to the `@Component` decorator.
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<code-example
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path="component-overview/src/app/component-overview/component-overview.component.ts"
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region="selector">
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</code-example>
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## Defining a component's template
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A template is a block of HTML that tells Angular how to render the component in your application.
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You can define a template for your component in one of two ways: by referencing an external file, or directly within the component.
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To define a template as an external file, add a `templateUrl` property to the `@Component` decorator.
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<code-example
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path="component-overview/src/app/component-overview/component-overview.component.ts"
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region="templateUrl">
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</code-example>
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To define a template within the component, add a `template` property to the `@Component` decorator that contains the HTML you want to use.
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<code-example
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path="component-overview/src/app/component-overview/component-overview.component.1.ts"
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region="template">
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</code-example>
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If you want your template to span multiple lines, you can use backticks (<code> ` </code>).
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For example:
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<code-example
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path="component-overview/src/app/component-overview/component-overview.component.2.ts"
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region="templatebacktick">
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</code-example>
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<div class="alert is-helpful">
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An Angular component requires a template defined using `template` or `templateUrl`. You cannot have both statements in a component.
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</div>
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## Declaring a component's styles
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You can declare component styles uses for its template in one of two ways: by referencing an external file, or directly within the component.
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To declare the styles for a component in a separate file, add a `styleUrls` property to the `@Component` decorator.
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<code-example
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path="component-overview/src/app/component-overview/component-overview.component.ts"
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region="decorator">
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</code-example>
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To declare the styles within the component, add a `styles` property to the `@Component` decorator that contains the styles you want to use.
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<code-example
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path="component-overview/src/app/component-overview/component-overview.component.3.ts"
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region="styles">
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</code-example>
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The `styles` property takes an array of strings that contain the CSS rule declarations.
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## Next steps
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* For an architectural overview of components, see [Introduction to components and templates](guide/architecture-components).
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* For additional options you can use when creating a component, see [Component](api/core/Component) in the API Reference.
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* For more information on styling components, see [Component styles](guide/component-styles).
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* For more information on templates, see [Template syntax](guide/template-syntax).
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