Global properties and methods in Vue - Mini Project: Build & Apply

Using Global Properties and Methods in Vue 3

📖 Scenario: You are building a simple Vue 3 app where you want to use a global property and a global method across components.This helps keep your code clean and reuse common values and functions easily.

🎯 Goal: Create a Vue 3 app that sets a global property called $appName with the value 'My Vue App' and a global method called $greet that returns a greeting string.Use these global features inside a component to display the app name and a greeting message.

📋 What You'll Learn

Create a Vue app using createApp

Add a global property $appName with value 'My Vue App'

Add a global method $greet that returns 'Hello from global method!'

Use these global features inside the component's template

💡 Why This Matters

🌍 Real World

Global properties and methods let you share common data and functions easily in Vue apps, like app name, theme colors, or utility functions.

💼 Career

Understanding global properties and methods is important for building scalable Vue applications and working on team projects where shared data and functions reduce repetition.

1

Create the Vue app and component

Create a Vue app using createApp and define a component called App with a template that contains a <div> with the text Welcome to Vue!.

Vue

import { createApp } from 'vue'

const App = {
  template: `Welcome to Vue!`
}

// Your code here

Hint

Use createApp(App) to create the app and app.mount('#app') to mount it.

2

Add a global property $appName

Add a global property called $appName to the Vue app instance and set its value to 'My Vue App'.

Vue

import { createApp } from 'vue'

const App = {
  template: `Welcome to Vue!`
}

const app = createApp(App)
// Add global property $appName here

app.mount('#app')

Hint

Use app.config.globalProperties to add global properties.

3

Add a global method $greet

Add a global method called $greet to the Vue app instance that returns the string 'Hello from global method!'.

Vue

import { createApp } from 'vue'

const App = {
  template: `Welcome to Vue!`
}

const app = createApp(App)
app.config.globalProperties.$appName = 'My Vue App'
// Add global method $greet here

app.mount('#app')

Hint

Assign a function to app.config.globalProperties.$greet that returns the greeting string.

4

Use global property and method in the component template

Update the App component template to display the global property $appName inside an <h1> and call the global method $greet() inside a <p>.

Vue

import { createApp } from 'vue'

const App = {
  template: `
    
       -->
       -->
    
  `
}

const app = createApp(App)
app.config.globalProperties.$appName = 'My Vue App'
app.config.globalProperties.$greet = () => 'Hello from global method!'
app.mount('#app')

Hint

Use {{ $appName }} and {{ $greet() }} inside the template to access global property and method.

Practice

1. What is the main purpose of app.config.globalProperties in Vue?

easy

A. To add properties or methods accessible in all components

B. To register new components globally

C. To configure routing paths

D. To define component-specific data

Solution

1. Step 1: Understand the role of app.config.globalProperties

   This object allows adding properties or methods that every Vue component can access easily.

2. Step 2: Differentiate from other Vue features

   Registering components, routing, and component data are handled differently, not via globalProperties.

3. Final Answer:

   To add properties or methods accessible in all components -> Option A

4. Quick Check:

   Global properties = shared access across components [OK]

Hint: Global properties share code across all components [OK]

Common Mistakes:

• Confusing globalProperties with component registration
• Thinking it configures routing
• Assuming it stores component local data

2. Which of the following is the correct way to add a global method named logMessage in Vue 3?

easy

A. app.globalProperties.logMessage = () => console.log('Hi')

B. app.config.globalProperties.logMessage = function logMessage() { console.log('Hi') }

C. app.config.globalProperties.logMessage = () => console.log('Hi')

D. app.config.globalProperties.$logMessage = () => console.log('Hi')

Solution

1. Step 1: Recall the correct syntax for global properties

   Global properties must be added to app.config.globalProperties with a $ prefix on the property name.

2. Step 2: Check the options for correct prefix and assignment

   app.config.globalProperties.$logMessage = () => console.log('Hi') correctly uses app.config.globalProperties.$logMessage with an arrow function.

3. Final Answer:

   app.config.globalProperties.$logMessage = () => console.log('Hi') -> Option D

4. Quick Check:

   Use app.config.globalProperties.$name for globals [OK]

Hint: Global properties need $ prefix and app.config [OK]

Common Mistakes:

• Omitting the $ prefix
• Using app.globalProperties instead of app.config.globalProperties
• Assigning without a function

3. Given this setup in main.js:

app.config.globalProperties.$greet = (name) => `Hello, ${name}!`

What will be the output of this code inside a component method?

console.log(this.$greet('Alice'))

medium

A. undefined

B. Hello, Alice!

C. Error: $greet is not a function

D. Hello, ${name}!

Solution

1. Step 1: Understand the global method definition

   The method $greet is defined globally to return a greeting string with the passed name.

2. Step 2: Analyze the component call

   Calling this.$greet('Alice') invokes the global method, returning Hello, Alice!.

3. Final Answer:

   Hello, Alice! -> Option B

4. Quick Check:

   Global method call returns expected string [OK]

Hint: Global methods run with this.$name inside components [OK]

Common Mistakes:

• Expecting template literal without interpolation
• Forgetting to use this.$ prefix
• Assuming method is undefined

4. Identify the error in this Vue 3 global property setup:

app.config.globalProperties.log = function(message) {
  console.log(message)
}

// Usage in component:
this.$log('Test')

medium

A. Missing $ prefix in global property name

B. Function syntax is incorrect

C. Cannot use global properties inside components

D. Should use arrow function instead of regular function

Solution

1. Step 1: Check the global property name

   The property is named log but used as $log in the component, causing mismatch.

2. Step 2: Understand Vue global property naming convention

   Global properties must be defined with a $ prefix to match usage in components.

3. Final Answer:

   Missing $ prefix in global property name -> Option A

4. Quick Check:

   Global properties need $ prefix to match usage [OK]

Hint: Global property name and usage must both have $ prefix [OK]

Common Mistakes:

• Defining without $ but using with $
• Thinking function syntax is wrong
• Believing global properties can't be used in components

5. You want to create a global property $formatDate that formats a Date object to YYYY-MM-DD. Which is the best way to define and use it in Vue 3?

hard

A. Add a global variable formatDate in main.js and use formatDate(date) in components

B. Create a component method named formatDate and call this.formatDate(date)

C. Define in app.config.globalProperties.$formatDate as a function returning formatted string; call with this.$formatDate(date) in components

D. Use a computed property in each component to format dates

Solution

1. Step 1: Understand global property usage

   Global properties are added to app.config.globalProperties with a $ prefix and accessed via this.$name in components.

2. Step 2: Evaluate options for best practice

   Define in app.config.globalProperties.$formatDate as a function returning formatted string; call with this.$formatDate(date) in components correctly defines the formatter globally and uses it properly in components, promoting code reuse.

3. Final Answer:

   Define in app.config.globalProperties.$formatDate as a function returning formatted string; call with this.$formatDate(date) in components -> Option C

4. Quick Check:

   Global reusable methods use $ prefix and app.config [OK]

Hint: Use app.config.globalProperties with $ prefix for reusable methods [OK]

Common Mistakes:

• Defining methods only inside components losing reuse
• Using global variables without Vue context
• Not using $ prefix for global properties