Vue.js v-show Directive

Introduction

When building interactive web applications, one of the most common needs is to show or hide elements based on certain conditions. Vue.js offers two primary ways to handle this: the v-if directive and the v-show directive.

In this tutorial, we'll focus on the v-show directive, which is a simple yet powerful tool for toggling an element's visibility without removing it from the DOM. This is particularly useful for elements that need to be toggled frequently, as it has better performance implications than repeatedly adding and removing elements.

What is the v-show Directive?

The v-show directive is used to conditionally display an element based on the truthiness of an expression. Unlike v-if which actually creates or destroys elements, v-show simply toggles the CSS display property of the element.

Basic Syntax

html

<element v-show="condition">Content</element>

When the condition evaluates to a truthy value, the element will be visible. When it evaluates to a falsy value, the element will be hidden (but still present in the DOM).

How v-show Works

Under the hood, v-show works by manipulating the CSS display property of an element:

• When the condition is true, the element is displayed normally (no inline style)
• When the condition is false, the element is hidden with display: none

Let's see a basic example:

html

<template>
  <div>
    <p v-show="isVisible">This text will be visible based on the value of isVisible</p>
    <button @click="toggleVisibility">Toggle Visibility</button>
  </div>
</template>

<script>
export default {
  data() {
    return {
      isVisible: true
    }
  },
  methods: {
    toggleVisibility() {
      this.isVisible = !this.isVisible;
    }
  }
}
</script>

In this example, clicking the button will toggle the visibility of the paragraph by switching the isVisible data property between true and false.

v-show vs v-if: Understanding the Difference

It's important to understand when to use v-show versus v-if:

Feature	v-show	v-if
Initial cost	Higher (element is always rendered)	Lower (element not rendered if condition is initially false)
Toggle cost	Lower (just toggles CSS property)	Higher (creates/destroys DOM elements)
DOM presence	Always present, just hidden	Only present when condition is true
Template compilation	Always compiled	Lazy compiled
Suitable for	Elements toggled frequently	Elements rarely toggled

Visual Representation

Practical Examples

Example 1: Simple Toggle Button

html

<template>
  <div class="container">
    <div v-show="isDetailsVisible" class="details-panel">
      <h2>User Details</h2>
      <p><strong>Name:</strong> John Doe</p>
      <p><strong>Email:</strong> john@example.com</p>
      <p><strong>Role:</strong> Administrator</p>
    </div>
    
    <button @click="isDetailsVisible = !isDetailsVisible">
      {{ isDetailsVisible ? 'Hide Details' : 'Show Details' }}
    </button>
  </div>
</template>

<script>
export default {
  data() {
    return {
      isDetailsVisible: false
    }
  }
}
</script>

<style scoped>
.details-panel {
  border: 1px solid #ddd;
  padding: 15px;
  margin-bottom: 10px;
  border-radius: 4px;
}
</style>

This example shows a details panel that can be toggled with a button. When hiding the panel, it's still in the DOM but not visible.

Example 2: Mobile Menu Toggle

html

<template>
  <div class="navbar">
    <div class="logo">MySite</div>
    
    <!-- Desktop Navigation (always visible) -->
    <nav class="desktop-nav">
      <a href="#home">Home</a>
      <a href="#about">About</a>
      <a href="#services">Services</a>
      <a href="#contact">Contact</a>
    </nav>
    
    <!-- Mobile Navigation Toggle Button -->
    <button class="menu-toggle" @click="isMobileMenuOpen = !isMobileMenuOpen">
      ☰ Menu
    </button>
    
    <!-- Mobile Navigation Dropdown -->
    <nav v-show="isMobileMenuOpen" class="mobile-nav">
      <a href="#home">Home</a>
      <a href="#about">About</a>
      <a href="#services">Services</a>
      <a href="#contact">Contact</a>
    </nav>
  </div>
</template>

<script>
export default {
  data() {
    return {
      isMobileMenuOpen: false
    }
  }
}
</script>

<style scoped>
.navbar {
  display: flex;
  flex-wrap: wrap;
  justify-content: space-between;
  padding: 15px;
  background: #333;
  color: white;
}

.desktop-nav {
  display: none;
}

.mobile-nav {
  width: 100%;
  background: #444;
  padding: 10px;
}

.mobile-nav a {
  display: block;
  padding: 10px;
  color: white;
  text-decoration: none;
}

.menu-toggle {
  background: none;
  border: none;
  color: white;
  font-size: 20px;
  cursor: pointer;
}

@media (min-width: 768px) {
  .desktop-nav {
    display: block;
  }
  .menu-toggle, .mobile-nav {
    display: none !important;
  }
}
</style>

This example shows a common mobile navigation pattern. On mobile devices, the menu is hidden by default and can be toggled with a button. Note how v-show is perfect for this use case because the menu will be toggled frequently.

Example 3: Form Field Conditionals

html

<template>
  <div class="form-container">
    <h2>Registration Form</h2>
    
    <div class="form-group">
      <label for="account-type">Account Type:</label>
      <select id="account-type" v-model="accountType">
        <option value="personal">Personal</option>
        <option value="business">Business</option>
      </select>
    </div>
    
    <!-- Basic fields for all account types -->
    <div class="form-group">
      <label for="name">Name:</label>
      <input type="text" id="name">
    </div>
    
    <div class="form-group">
      <label for="email">Email:</label>
      <input type="email" id="email">
    </div>
    
    <!-- Business-specific fields -->
    <div v-show="accountType === 'business'">
      <h3>Business Information</h3>
      
      <div class="form-group">
        <label for="company-name">Company Name:</label>
        <input type="text" id="company-name">
      </div>
      
      <div class="form-group">
        <label for="tax-id">Tax ID:</label>
        <input type="text" id="tax-id">
      </div>
      
      <div class="form-group">
        <label for="industry">Industry:</label>
        <select id="industry">
          <option value="tech">Technology</option>
          <option value="retail">Retail</option>
          <option value="healthcare">Healthcare</option>
          <option value="other">Other</option>
        </select>
      </div>
    </div>
    
    <button type="submit">Register</button>
  </div>
</template>

<script>
export default {
  data() {
    return {
      accountType: 'personal'
    }
  }
}
</script>

<style scoped>
.form-container {
  max-width: 500px;
  margin: 0 auto;
  padding: 20px;
}

.form-group {
  margin-bottom: 15px;
}

label {
  display: block;
  margin-bottom: 5px;
}

input, select {
  width: 100%;
  padding: 8px;
  border: 1px solid #ddd;
  border-radius: 4px;
}

button {
  background-color: #4CAF50;
  color: white;
  padding: 10px 15px;
  border: none;
  border-radius: 4px;
  cursor: pointer;
}
</style>

In this example, we use v-show to conditionally display business-specific form fields when the user selects "Business" as their account type. Since users might switch back and forth between account types during registration, using v-show is more efficient than v-if here.

Best Practices for Using v-show

1. Use v-show for frequently toggled elements: If an element will be hidden and shown many times, v-show is more efficient.

2. Consider initial page load: If an element is likely to be hidden when the page loads and for a long time afterward, consider using v-if instead to avoid rendering it initially.

3. Combine with computed properties: For complex conditions, use a computed property:

html

<template>
  <div v-show="shouldShowDashboard">
    <!-- Dashboard content -->
  </div>
</template>

<script>
export default {
  data() {
    return {
      userRole: 'guest',
      isLoggedIn: false
    }
  },
  computed: {
    shouldShowDashboard() {
      return this.isLoggedIn && (this.userRole === 'admin' || this.userRole === 'manager');
    }
  }
}
</script>

4. Remember that v-show doesn't support <template> or v-else: Unlike v-if, you can't use v-show with <template> tags or with v-else.

5. Consider accessibility: Elements hidden with v-show are still in the DOM, so ensure that hidden interactive elements aren't accidentally focusable via keyboard navigation.

Summary

The v-show directive in Vue.js is a powerful tool for conditionally displaying elements based on changing conditions. It works by toggling the CSS display property rather than actually adding or removing elements from the DOM.

Key points to remember:

• Use v-show for elements that will be toggled frequently
• v-show has higher initial render cost but lower toggle cost compared to v-if
• Elements with v-show are always rendered in the DOM, just hidden when the condition is false
• v-show doesn't support <template> tags or v-else directives

By understanding the differences between v-show and v-if, you can make better decisions about which directive to use in different scenarios, leading to better performance and user experience in your Vue applications.

Exercises

1. Create a simple image gallery where clicking on a thumbnail shows a larger version of the image using v-show.
2. Build a tabbed interface where clicking on different tab buttons shows different content panels.
3. Implement a FAQ page where clicking on questions toggles the visibility of answers.
4. Create a form with conditional sections that appear based on previous selections.
5. Compare the performance of v-show vs v-if in a scenario with 100 elements being toggled repeatedly.

Additional Resources

• Vue.js Official Documentation on v-show
• Vue.js Guide on Conditional Rendering
• Performance Comparison: v-if vs v-show