📦 Vue Props – Pass Data Between Components in Vue.js (2025 Guide)

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🧲 Introduction – What Are Props in Vue?

In Vue.js, props (short for properties) are the primary way to pass data from a parent component to a child component. They form the backbone of Vue’s component communication system and are critical for creating reusable, modular components.

🎯 In this guide, you’ll learn:

• What props are and why they’re important
• How to define, pass, and validate props
• The difference between static and dynamic props
• Best practices and common mistakes

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📘 What Is a Prop in Vue?

A prop is a custom attribute on a child component tag that lets you pass data from the parent to the child.

✅ Basic Example:

<!-- Parent Component -->
<ChildComponent message="Hello from Parent" />

// ChildComponent.vue
props: ['message']

🧠 message will be available as a reactive variable inside the child.

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🧱 Defining Props in Components

✅ Using an Array (Simple Syntax)

props: ['title', 'count']

✅ Using an Object (Detailed with Validation)

props: {
  title: String,
  count: {
    type: Number,
    required: true,
    default: 0
  }
}

🧠 This allows type checking, defaults, and required flags.

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🔁 Passing Static vs Dynamic Props

✅ Static (Hardcoded):

<Alert message="Static Text" />

✅ Dynamic (Uses JavaScript variable):

<Alert :message="alertText" />

🧠 The : tells Vue to evaluate the expression instead of using a string literal.

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🧪 Full Working Example – Prop Communication

✅ Parent Component:

<ProductCard :product="item" />

data() {
  return {
    item: { name: 'Laptop', price: 999 }
  }
}

✅ Child Component (ProductCard.vue):

<template>
  <div>
    <h2>{{ product.name }}</h2>
    <p>${{ product.price }}</p>
  </div>
</template>

<script>
export default {
  props: ['product']
}
</script>

🧠 The child now displays information passed from the parent via product.

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⚠️ Common Prop Issues

❌ Using props as data (mutation):

// Avoid mutating props directly
this.message = 'Changed';

✅ Use a local copy if needed:

data() {
  return {
    localMessage: this.message
  };
}

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🛡️ Prop Type Validation and Defaults

Property	Purpose
type	Validates the prop type
default	Sets a fallback value if not provided
required	Throws warning if missing

✅ Example:

props: {
  price: {
    type: Number,
    default: 0,
    required: true
  }
}

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🔗 One-Way Data Flow

Props are one-way bound: data flows from parent ➝ child, not the other way.

This makes component communication predictable and easy to debug.

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📦 Real-World Example – Button with Label

✅ Reusable Button:

<template>
  <button>{{ label }}</button>
</template>

<script>
export default {
  props: {
    label: {
      type: String,
      required: true
    }
  }
}
</script>

✅ Parent:

<BaseButton label="Submit" />
<BaseButton label="Cancel" />

🧠 Easy-to-reuse component with different labels via props.

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🔁 Syncing Props with Events (v-model + modelValue)

In Vue 3, you can use v-model with props like modelValue:

✅ Child:

<template>
  <input :value="modelValue" @input="$emit('update:modelValue', $event.target.value)" />
</template>

<script>
export default {
  props: ['modelValue']
}
</script>

✅ Parent:

<TextInput v-model="name" />

🧠 Seamless two-way binding using props + emit.

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📌 Summary – Recap & Next Steps

Props in Vue are essential for passing data from parent to child components. They enable component reusability, logic separation, and maintainable architecture in Vue apps.

🔍 Key Takeaways:

• Props pass data downward from parent to child
• Use props: [] or an object with validation
• Props are read-only and one-way
• Use modelValue and $emit for two-way communication

⚙️ Real-World Relevance:
Props power dynamic interfaces like product cards, form inputs, alerts, dropdowns, and reusable UI components.

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❓ FAQ Section

❓ What is a prop in Vue?

✅ A prop is a way to pass data from a parent component to a child component via custom attributes.

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❓ How do I validate props?

✅ Use the object syntax:

props: {
  title: { type: String, required: true }
}

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❓ Are props reactive?

✅ Yes, props are reactive. If the parent updates the value, the child receives the new data automatically.

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❓ Can a child component modify a prop?

✅ No. Props are read-only. Use a local copy in data() if you need to modify it.

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❓ How to implement two-way binding with props?

✅ Use v-model with modelValue and emit update:modelValue from the child.

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