Which decorator is used to make a property reactive in LWC?

In Lightning Web Components (LWC), the decorator used to make a property reactive is @track. When you apply the @track decorator to a property in a component, it enables the component to re-render whenever the property's value changes. This is important for dynamic user interfaces that need to update based on user interactions or changes in underlying data.

The @track decorator ensures that the LWC engine is aware of changes to the property and can efficiently trigger a re-render of the component when necessary. Initially, @track was frequently used to mark properties of complex data types, such as objects or arrays, to monitor changes within them. However, with more recent updates, the reactivity in LWC has been enhanced, allowing for simpler state management and reducing the need for tracking certain properties explicitly.

The other decorators serve different purposes: @api is used for public properties that can be accessed by parent components, @wire is used for connecting a component to data from a Salesforce service, and @component is not a valid LWC decorator. Therefore, @track is the correct choice for making properties reactive in LWC.