vue js data property in component must be a function

In Vue, the data property in a component must be a function. This is because when a component is created, the same object is reused for all instances, which could lead to cross-instance state pollution if data is not a function. By making data a function, a new object is returned for each instance, ensuring that the state is properly isolated. This is a crucial aspect of Vue's reactivity system, as it allows Vue to track changes to the state and update the DOM accordingly. Therefore, it is important to define the data property as a function in Vue components to ensure proper state management and reactivity.