Vue Reactivity System: Data Binding u0026 Watchers Quiz Quiz

Explore your understanding of the Vue reactivity system with scenarios focused on data binding, computed properties, and reactive watchers. This quiz helps reinforce key concepts in reactive data handling and change detection in Vue applications.

1. Understanding Two-Way Data Binding

   In a reactive Vue system, which directive allows seamless two-way data binding between an input element and a reactive property named 'username'?

   1. v-for
   2. v-if
   3. v-model
   4. v-bind

   Explanation: The v-model directive provides two-way data binding for form inputs, ensuring changes in the input update the data property and vice versa. v-bind only binds data one way from the model to the view, not the other direction. v-for is used for rendering lists, not for data binding. v-if is used to conditionally render elements, not for binding data.

2. Computed Properties vs Watchers

   Given a component that calculates a user's full name from first and last name data fields, which feature is most appropriate for returning and updating the full name automatically whenever these fields change?

   1. Ref function
   2. Watcher
   3. Mounted hook
   4. Computed property

   Explanation: A computed property is ideal here because it is cached and only recalculates when its dependencies change, making it efficient for dynamic properties based on other reactive fields. A watcher is better for performing side effects on data changes, not for deriving values. Ref function is for creating reactive primitives, not for computed values. Mounted hook is for lifecycle control, not for dynamic property calculation.

3. Watchers for Side Effects

   If you need to perform an asynchronous API call each time the 'searchQuery' data property changes, what is the most suitable tool in the reactivity system?

   1. Watcher
   2. v-slot
   3. Transition group
   4. Prop validation

   Explanation: A watcher allows for running custom code, such as API calls, in response to reactive data changes, which is essential for handling asynchronous operations triggered by state updates. v-slot is for slot content injection, not reactivity. Prop validation is for checking incoming prop types, not handling changes. Transition group is related to visual transitions, not data change monitoring.

4. Reactivity in Nested Objects

   When updating a nested property, like 'user.profile.age', which issue must you be aware of to maintain reactivity in Vue's data system?

   1. Declaring the property as computed causes loss of reactivity
   2. Array mutations are not tracked at all
   3. Direct assignment to a nested property may not be reactive
   4. Using v-for on objects automatically makes properties reactive

   Explanation: Directly assigning values to deep properties can bypass the reactivity system, potentially leading to changes not being detected. Declaring properties as computed does not inherently cause loss of reactivity if set up properly. Using v-for makes lists reactive but not nested object properties. Array mutations are tracked, though caution is needed with specific mutation methods.

5. Limitation of Watchers

   Which scenario illustrates a limitation of watchers in Vue's reactivity system?

   1. Watchers cannot run side-effect code after data changes
   2. v-model does not work with custom components
   3. Deep changes in nested objects may require special configuration to be noticed
   4. Computed properties always trigger when any data changes in the component

   Explanation: Watchers do not, by default, observe deep changes in nested objects unless explicitly set to 'deep', which can lead to missed updates. Watchers are specifically designed to run side-effects, so option two is incorrect. Computed properties are only recalculated when their dependencies change, not for every data change. v-model can be made to work with custom components if the relevant binding is properly set up.