programming
beginner
10 sample questions
Vue MCQ Practice Test
Components, props, and state management in Vue
Q1. Within a Vue 3 component utilizing the Composition API, you're managing a reactive array of objects, each with a nested property 'count'. You need to efficiently update the 'count' property of only the object where the 'id' property matches a specific value. Which approach minimizes re-renders and offers the most performant update?
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A. Using Vue.set() to directly update the nested property
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B. Wrapping the array with reactive() and updating the nested 'count' property directly on the matched object ✓
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C. Leveraging $set() to modify the nested 'count' property after finding the matching object via findIndex()
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D. Iterating through the array with a for loop, identifying the object, and then directly updating the nested 'count' property
Explanation: Vue 3's Proxy-based reactivity tracks nested property writes automatically: make the array reactive(), find the matching object (e.g. with find/findIndex), and set obj.count = newValue - only components reading that property re-render. Vue.set() and $set() are Vue 2 APIs that do not exist in Vue 3, and a manual for loop offers no advantage over find().
Q2. What is the purpose of the `$forceUpdate()` method in a Vue.js component?
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A. It re-renders the entire component tree
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B. It updates the component's data property
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C. It triggers a re-render of the component ✓
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D. It resets the component's state
Explanation: The `$forceUpdate()` method is used to trigger a re-render of the component, which is useful when the component's state has changed but Vue.js is not able to detect it automatically. This method should be used sparingly, as it can cause performance issues if called too frequently.
Q3. In Vue, what is the purpose of the `$root` property within a child component?
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A. It is used to access the root instance of the application ✓
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B. It is used to access the parent instance of the current component
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C. It is used to access the global event bus
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D. It is used to access the Vue Devtools
Explanation: The `$root` property in Vue is used to access the root instance of the application, which is the top-level Vue instance. This can be useful when you need to access data or methods from the root instance within a child component.
Q4. In a Vue.js application, what is the purpose of the `$root` property in the `vm.$root` syntax?
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A. It is used to access the root instance of the Vue application from a child component ✓
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B. It is used to access the parent instance of the Vue application from a child component
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C. It is used to access the global event bus of the Vue application
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D. It is used to access the Vue DevTools debugger
Explanation: The `$root` property is a shortcut to the root instance of the Vue application, allowing you to access its data and methods from any child component.
Q5. How do you define an optional prop with a default value in a Vue component?
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A. By using the `v-bind` directive with a default value in the template.
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B. By using the `@` shorthand for event binding and providing a default value.
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C. By defining the prop with a `default` value in the component's `props` option. ✓
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D. By using the `:propname` syntax in the template and providing a default value.
Explanation: In Vue, to make a prop optional and provide a default value, you define the prop in the component's `props` option. For example:
```javascript
props: {
propname: {
type: String,
default: 'default'
}
}
```
This allows the component to use 'default' if no value is provided when the component is used.
Q6. In a Vue.js application, what is the purpose of the `$root` property in a child component?
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A. It allows the child component to access the root instance's data. ✓
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B. It allows the root instance to access the child component's data.
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C. It allows the child component to access the root instance's methods.
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D. It allows the child component to access the root instance's computed properties.
Explanation: The `$root` property in a Vue.js child component allows it to access the root instance's data. This is useful when a child component needs to access data from the root instance, but does not want to receive the data as a prop.
Q7. What is the purpose of the `$root` property in Vue.js?
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A. It is used to access the root instance of the application ✓
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B. It is used to access the parent instance of a component
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C. It is used to create a new instance of a component
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D. It is used to destroy an instance of a component
Explanation: The `$root` property in Vue.js allows you to access the root instance of the application from anywhere in the component tree. This can be useful when you need to access data or methods from the root instance in a child component.
Q8. Which Vue lifecycle hook is called immediately before the component is mounted?
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A. beforeCreate
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B. created
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C. beforeMount ✓
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D. mounted
Explanation: The `beforeMount` lifecycle hook is called right before the component is mounted to the DOM. It is used to perform any setup or configuration before the component is rendered.
Q9. What is the purpose of the "template" option in the Vue <script> tag?
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A. To define the HTML structure of the component ✓
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B. To register a global component
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C. To enable the use of JSX syntax
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D. To configure the component's lifecycle hooks
Explanation: The "template" option in the Vue <script> tag is used to define the HTML structure of the component. This is the recommended way to define the template in Vue, as it allows for better code organization and separation of concerns.
Q10. What is the purpose of the "$emit()" method in Vue.js?
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A. To update the component's props
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B. To emit an event to a parent component ✓
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C. To dispatch an action to a Vuex store
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D. To render a child component
Explanation: The "$emit()" method in Vue.js is used to emit an event to a parent component, allowing child components to communicate with their parent components.
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