angular/aio/content/tutorial/first-app/first-app-lesson-05.md

Lesson 5 - Add an input parameter to the component

This tutorial lesson demonstrates how to create a component @Input(), use it to pass data to a component for customization.

Time required: expect to spend about 10 minutes to complete this lesson.

Before you start

This lesson starts with the code from the previous lesson, so you can:

• Use the code that you created in Lesson 4 in your integrated development environment (IDE).
• Start with the code example from the previous lesson. Choose the from Lesson 4 where you can:
  • Use the live example in StackBlitz, where the StackBlitz interface is your IDE.
  • Use the download example and open it in your IDE.

If you haven't reviewed the introduction, visit the Introduction to Angular tutorial to make sure you have everything you need to complete this lesson.

If you have any trouble during this lesson, you can review the completed code for this lesson, in the for this lesson.

After you finish

• Your app has a new interface that it can use as a data type.
• Your app has an instance of the new interface with sample data.

Conceptual preview of Inputs

Inputs allow components to share data. The direction of the data sharing is from parent component to child component.

To receive data from a parent component, a child component must mark a class property with the @Input() decorator. This decorator can be used in components and directives.

For a more in depth explanation, please refer to the Sharing data between child and parent directives and components guide.

In this lesson, you'll define @Input() properties in the HousingLocationComponent component which will enable you to customize the data displayed in the component.

Lesson steps

Perform these steps on the app code in your IDE.

Step 1 - Import the Input decorator

This step imports the Input decorator into the class.

In the code editor:

1. Navigate to src/app/housing-location/housing-location.component.ts

2. Update the file imports to include Input and HousingLocation:

Step 2 - Add the Input property

1. In the same file, add a property called housingLocation of type HousingLocation to the HousingLocationComponent class. Add an ! after the property name and prefix it with the @Input() decorator:

   You have to add the ! because the input is expecting the value to be passed. In this case, there is no default value. In our example application case we know that the value will be passed in - this is by design. The exclamation point is called the non-null assertion operator and it tells the TypeScript compiler that the value of this property won't be null or undefined.

2. Save your changes and confirm the app does not have any errors.

3. Correct any errors before you continue to the next step.

Lesson review

In this lesson, you created a new property decorated with the @Input() decorator. You also used the non-null assertion operator to notify the compiler that the value of the new property won't be null or undefined.

If you are having any trouble with this lesson, you can review the completed code for it in the .

Next steps

• Lesson 6 - Add a property binding to an component’s template

For more information about the topics covered in this lesson, visit:

• Sharing data between child and parent directives and components