Props for parent to child data in Vue - Mini Project: Build & Apply

Props for parent to child data

📖 Scenario: You are building a simple Vue app that shows a greeting message. The parent component holds the message text. The child component will receive this message as a prop and display it.

🎯 Goal: Create a parent component that passes a greeting message to a child component using props. The child component should display the message inside a paragraph.

📋 What You'll Learn

Create a parent component named ParentComponent with a data property greeting set to 'Hello from Parent!'.

Create a child component named ChildComponent that accepts a prop named message.

Use the ChildComponent inside ParentComponent and pass the greeting data as the message prop.

Display the message prop inside a <p> tag in ChildComponent.

💡 Why This Matters

🌍 Real World

Passing data from parent to child components is a common pattern in Vue apps to keep components reusable and organized.

💼 Career

Understanding props is essential for building interactive Vue applications and collaborating in frontend development teams.

1

Set up the parent component data

Create a Vue component named ParentComponent with a data function that returns an object containing a property greeting set to the string 'Hello from Parent!'.

Vue

export default {
  name: 'ParentComponent',
  // Your code here
}

Hint

Remember, the data option in Vue components is a function that returns an object with your data properties.

2

Create the child component with a prop

Create a Vue component named ChildComponent that declares a prop named message.

Vue

export default {
  name: 'ParentComponent',
  data() {
    return {
      greeting: 'Hello from Parent!'
    };
  }
}

// Your code here to create ChildComponent with prop 'message'

Hint

Use the props option to declare props in Vue components as an array of strings.

3

Use the child component in the parent and pass the prop

Inside ParentComponent, register ChildComponent in the components option. Then, in the template, use <ChildComponent :message="greeting" /> to pass the greeting data as the message prop.

Vue

  



export default {
  name: 'ParentComponent',
  data() {
    return {
      greeting: 'Hello from Parent!'
    };
  },
  components: {
    ChildComponent
  }
}

export const ChildComponent = {
  name: 'ChildComponent',
  props: ['message']
};

Hint

Remember to register the child component in the components option and use the :message="greeting" binding in the template.

4

Display the prop message in the child component template

Add a template section to ChildComponent that displays the message prop inside a <p> tag.

Vue

  



export const ChildComponent = {
  name: 'ChildComponent',
  props: ['message'],
  // Your code here to add template
};

export default {
  name: 'ParentComponent',
  data() {
    return {
      greeting: 'Hello from Parent!'
    };
  },
  components: {
    ChildComponent
  }
};

Hint

Use the template property in the child component object to define the HTML that uses the message prop.

Practice

1. What is the main purpose of props in Vue components?

easy

A. To pass data from a parent component to a child component

B. To store local state inside a component

C. To handle user input events

D. To define methods inside a component

Solution

1. Step 1: Understand the role of props

   Props are designed to send data from a parent component down to its child components.

2. Step 2: Differentiate props from other features

   Local state stores data inside a component, events handle user actions, and methods define functions. Only props pass data downward.

3. Final Answer:

   To pass data from a parent component to a child component -> Option A

4. Quick Check:

   Props = Parent to Child Data [OK]

Hint: Props always send data from parent to child [OK]

Common Mistakes:

• Confusing props with local state
• Thinking props handle events
• Assuming props define methods

2. Which of the following is the correct way to declare a prop named title in a Vue 3 child component using <script setup>?

easy

A. const props = defineProps({ title: String })

B. props: ['title']

C. export default { props: ['title'] }

D. const title = ref('')

Solution

1. Step 1: Identify Vue 3 <script setup> syntax

   In Vue 3 with <script setup>, props are declared using defineProps().

2. Step 2: Match the correct syntax for prop declaration

   const props = defineProps({ title: String }) correctly declares a prop named title of type String.

3. Final Answer:

   const props = defineProps({ title: String }) -> Option A

4. Quick Check:

   Vue 3 <script setup> uses defineProps() [OK]

Hint: Use defineProps() inside

Common Mistakes:

• Using options API syntax inside
• Declaring props as local refs
• Forgetting to use defineProps() in

3. Given the parent component template:

<ChildComponent :message="'Hello Vue'" />

And the child component script setup:

const props = defineProps({ message: String })
console.log(props.message)

What will be logged to the console?

medium

A. undefined

B. 'Hello Vue'

C. An error because props.message is read-only

D. null

Solution

1. Step 1: Understand prop passing

   The parent passes the string 'Hello Vue' as the message prop to the child.

2. Step 2: Accessing the prop in child

   The child uses defineProps to declare message and logs props.message, which holds 'Hello Vue'.

3. Final Answer:

   'Hello Vue' -> Option B

4. Quick Check:

   Passed prop value logs correctly [OK]

Hint: Props hold passed values, accessible via props object [OK]

Common Mistakes:

• Expecting props to be undefined without declaration
• Confusing read-only with inaccessible
• Assuming props are null if not reactive

4. What is wrong with this child component code that tries to modify a prop?

<script setup>
const props = defineProps({ count: Number })
props.count = props.count + 1
</script>

medium

A. Props must be declared as reactive refs to modify

B. The prop type Number is invalid in defineProps

C. Missing import of defineProps

D. Props are read-only and cannot be assigned new values

Solution

1. Step 1: Recall prop immutability

   Props in Vue are read-only inside child components and cannot be directly modified.

2. Step 2: Identify the error in code

   The code tries to assign a new value to props.count, which violates the read-only rule and causes an error.

3. Final Answer:

   Props are read-only and cannot be assigned new values -> Option D

4. Quick Check:

   Props cannot be changed inside child [OK]

Hint: Never assign new values to props inside child [OK]

Common Mistakes:

• Trying to mutate props directly
• Confusing props with reactive state
• Ignoring Vue warnings about prop mutation

5. You want to pass a list of user names from a parent to a child component and display them. Which approach correctly passes and uses the prop in the child component using Vue 3 <script setup>?

Parent template:

<UserList :users="['Alice', 'Bob', 'Charlie']" />

Choose the correct child component code:

hard

A. <script setup>
export default {
props: ['users']
}
</script>
<template>
<ul>
<li v-for="user in users" :key="user">{{ user }}</li>
</ul>
</template>

B. <script setup>
const users = ref([])
</script>
<template>
<ul>
<li v-for="user in users" :key="user">{{ user }}</li>
</ul>
</template>

C. <script setup>
const props = defineProps({ users: Array })
</script>
<template>
<ul>
<li v-for="user in props.users" :key="user">{{ user }}</li>
</ul>
</template>

D. <script setup>
const props = defineProps({ users: String })
</script>
<template>
<ul>
<li v-for="user in props.users" :key="user">{{ user }}</li>
</ul>
</template>

Solution

1. Step 1: Check prop declaration type

   The parent passes an array, so the child must declare users as type Array using defineProps({ users: Array }).

2. Step 2: Verify template usage

   The child uses v-for to loop over props.users and display each user in a list item, which is correct.

3. Final Answer:

   The code using defineProps({ users: Array }) and v-for on props.users -> Option C

4. Quick Check:

   Array prop with defineProps and v-for works [OK]

Hint: Match prop type to passed data and loop in template [OK]

Common Mistakes:

• Declaring wrong prop type (e.g., String instead of Array)
• Not using defineProps in
• Trying to mutate props inside child