Configure Vue App Before Calling mount()

Impact: HIGH - Any app configurations applied after .mount() is called are silently ignored. This includes error handlers, global components, directives, and plugins, leading to mysterious missing functionality.

The .mount() method should always be called after all app configurations and asset registrations are done. This is a critical ordering requirement that, when violated, produces no errors but causes features to silently fail.

Task Checklist

• [ ] Register all plugins (router, store, etc.) before mount()
• [ ] Configure error handlers before mount()
• [ ] Register global components and directives before mount()
• [ ] Set all app.config properties before mount()
• [ ] Call .mount() as the final step in app initialization

Incorrect:

import { createApp } from 'vue'
import App from './App.vue'
import router from './router'

const app = createApp(App)

// WRONG: Mounting first, then configuring
app.mount('#app')

// These are silently IGNORED - app is already mounted!
app.use(router)
app.config.errorHandler = (err) => {
  console.error('Global error:', err)
}
app.component('GlobalButton', GlobalButton)

Correct:

import { createApp } from 'vue'
import App from './App.vue'
import router from './router'
import { createPinia } from 'pinia'
import GlobalButton from './components/GlobalButton.vue'

const app = createApp(App)

// Configure everything FIRST
app.use(router)
app.use(createPinia())

// Set up error handling
app.config.errorHandler = (err, instance, info) => {
  console.error('Global error:', err)
  console.log('Component:', instance)
  console.log('Error info:', info)
}

// Register global components
app.component('GlobalButton', GlobalButton)

// Mount LAST - after all configuration is complete
app.mount('#app')

Common Mistake: Chaining with Mount

// WRONG: Chaining mount in the middle of configuration
createApp(App)
  .use(router)
  .mount('#app')  // Everything after this line is a problem
  .use(pinia)     // This doesn't even work - mount returns component instance!

// CORRECT: Either complete chain before mount, or use intermediate variable
createApp(App)
  .use(router)
  .use(pinia)
  .component('GlobalButton', GlobalButton)
  .mount('#app')  // Mount at the very end

Reference

• Vue.js - Creating a Vue Application
• Vue.js Application API