To create an interface in Angular, generate a TypeScript interface with Angular CLI, describe the object’s properties, then import the interface and use it as the type for a component property. For example, an interface can define the shape of housing-location data so TypeScript can catch mismatched fields while you build the app.
What an Angular interface does
An interface is a TypeScript type that describes the shape of an object. Angular’s tutorial puts it simply: “Interfaces are custom data types for your app.” An interface is not an Angular component and does not render anything; it gives application code a shared description of data.
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That distinction matters: a component class can hold data, and its template can display that data, but the interface only describes what the data should look like. Type checking can reveal mismatches in your code, but a TypeScript interface does not validate an external API response at runtime.
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Generate an interface with Angular CLI
From your Angular project directory, run:
ng generate interface housinglocationThe CLI creates an interface file in the project. The shorter command is ng generate i housinglocation. See the Angular CLI interface command for its syntax and options.
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Define the object shape
In the generated file, define the properties that each housing-location object must have. The Angular first-app tutorial uses this interface:
export interface HousingLocationInfo {
id: number;
name: string;
city: string;
state: string;
photo: string;
availableUnits: number;
wifi: boolean;
laundry: boolean;
}Each property name and type is part of the contract: for example, availableUnits must be a number and wifi must be a boolean. Adjust the shape to match your app’s data rather than adding properties solely because they appear in this example.
Import the interface and type a component property
Import HousingLocationInfo into the component that will hold a location, then annotate the property and assign an object that conforms to the interface:
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import { HousingLocationInfo } from '../housinglocation';
@Component({
selector: 'app-housing-location',
template: `<h2>{{ housingLocation.name }}</h2>`,
})
export class HousingLocationComponent {
housingLocation: HousingLocationInfo = {
id: 1,
name: 'Test location',
city: 'Test city',
state: 'TS',
photo: '/assets/example.jpg',
availableUnits: 4,
wifi: true,
laundry: false,
};
}Use the import path that matches where the CLI generated the file in your project. The assigned object needs every required property with a compatible type; omitting a required field or assigning a string where a number is expected produces a type error. The Angular tutorial’s interface lesson walks through the same define–import–use sequence.
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How the interface relates to the template
Angular components combine a TypeScript class, an HTML template, and a selector, with configuration supplied through @Component. The class holds data and behavior; the template renders the interface users see. In the example, {{ housingLocation.name }} reads a value from the typed object, but the interface itself creates no visible UI. See Angular’s guides to component anatomy and templates.
Templates can also bind properties and attributes, respond to events, conditionally show content with @if/@else, and repeat content with @for. Those features determine how data is presented and interacted with; the interface helps describe the data the component uses. Angular’s template essentials explain these patterns.
What type checking can—and cannot—catch
- It can catch code-level shape mistakes: incompatible property types and missing required properties are reported by TypeScript tooling.
- It cannot check data at runtime: an interface is not a validator for JSON received from an API or other untrusted source. Validate external data separately before relying on it.
When a form is part of the interface
If users can edit data, the form approach is a separate decision from the interface that describes the data object. Angular’s forms guide recommends reactive forms when forms are central to the app or when reactive patterns are already in use: they provide direct access to the form model and support scalable, reusable, testable code. Template-driven forms are a straightforward fit for basic forms managed in the template. Choose based on complexity and how much form behavior your app needs.
Accessibility still needs attention
A well-typed data object does not make a rendered interface accessible by itself. Use semantic HTML and bind accessibility-related attributes where needed. Angular documents tools such as Angular Material components and CDK accessibility utilities, including LiveAnnouncer and cdkTrapFocus; these can support particular interactions but do not replace accessibility testing. See Angular’s accessibility guidance.
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