angular/aio/content/guide/property-binding.md

Property binding

Property binding in Angular helps you set values for properties of HTML elements or directives. Use property binding to do things such as toggle button features, set paths programmatically, and share values between components.

See the for a working example containing the code snippets in this guide.

Prerequisites

• Basics of components
• Basics of templates
• Binding syntax

Understanding the flow of data

Property binding moves a value in one direction, from a component's property into a target element property.

To read a target element property or call one of its methods, see the API reference for ViewChild and ContentChild.

Binding to a property

For information on listening for events, see Event binding.

To bind to an element's property, enclose it in square brackets, [], which identifies the property as a target property.

A target property is the DOM property to which you want to assign a value.

To assign a value to a target property for the image element's src property, type the following code:

In most cases, the target name is the name of a property, even when it appears to be the name of an attribute.

In this example, src is the name of the <img> element property.

The brackets, [], cause Angular to evaluate the right-hand side of the assignment as a dynamic expression.

Without the brackets, Angular treats the right-hand side as a string literal and sets the property to that static value.

To assign a string to a component's property (such as the childItem of the ItemDetailComponent), you use the same bracket assignment notation:

Setting an element property to a component property value

To bind the src property of an <img> element to a component's property, place src in square brackets followed by an equal sign and then the property.

Using the property itemImageUrl, type the following code:

Declare the itemImageUrl property in the class, in this case AppComponent.

{@a colspan}

colspan and colSpan

A common point of confusion is between the attribute, colspan, and the property, colSpan. Notice that these two names differ by only a single letter.

To use property binding using colSpan, type the following:

To disable a button while the component's isUnchanged property is true, type the following:

To set a property of a directive, type the following:

To set the model property of a custom component for parent and child components to communicate with each other, type the following:

Toggling button features

To use a Boolean value to disable a button's features, bind the disabled DOM attribute to a Boolean property in the class.

Because the value of the property isUnchanged is true in the AppComponent, Angular disables the button.

What's next

• Property binding best practices
• Event binding
• Text Interpolation
• Class & Style Binding
• Attribute Binding

@reviewed 2023-09-01