/vue-best-practices

Vue Plugin Best Practices

Impact: MEDIUM - Vue plugins should follow the app.use() contract, expose explicit capabilities, and use collision-safe injection keys. This keeps plugin setup predictable and composable across large apps.

Task List

• Export plugins as an object with install() or as an install function
• Use the app instance in install() to register components/directives/provides
• Type plugin APIs with Plugin (and options tuple types when needed)
• Use symbol keys (prefer InjectionKey<T>) for provide/inject in plugins
• Add a small typed composable wrapper for required injections to fail fast

Structure Plugins for app.use()

A Vue plugin must be either:

• An object with install(app, options?)
• A function with the same signature

BAD:

const notAPlugin = {
  doSomething() {}
}

app.use(notAPlugin)

GOOD:

import type { App } from 'vue'

interface PluginOptions {
  prefix?: string
  debug?: boolean
}

const myPlugin = {
  install(app: App, options: PluginOptions = {}) {
    const { prefix = 'my', debug = false } = options

    if (debug) {
      console.log('Installing myPlugin with prefix:', prefix)
    }

    app.provide('myPlugin', { prefix })
  }
}

app.use(myPlugin, { prefix: 'custom', debug: true })

GOOD:

import type { App } from 'vue'

function simplePlugin(app: App, options?: { message: string }) {
  app.config.globalProperties.$greet = () => options?.message ?? 'Hello!'
}

app.use(simplePlugin, { message: 'Welcome!' })

Register Capabilities Explicitly in install()

Inside install(), wire behavior through Vue application APIs:

• app.component() for global components
• app.directive() for global directives
• app.provide() for injectable services and config
• app.config.globalProperties for optional global helpers (sparingly)

BAD:

const uselessPlugin = {
  install(app, options) {
    const service = createService(options)
  }
}

GOOD:

const usefulPlugin = {
  install(app, options) {
    const service = createService(options)
    app.provide(serviceKey, service)
  }
}

Type Plugin Contracts

Use Vue's Plugin type to keep install signatures and options type-safe.

import type { App, Plugin } from 'vue'

interface MyOptions {
  apiKey: string
}

const myPlugin: Plugin<[MyOptions]> = {
  install(app: App, options: MyOptions) {
    app.provide(apiKeyKey, options.apiKey)
  }
}

Use Symbol Injection Keys in Plugins

String keys can collide ('http', 'config', 'i18n'). Use symbol keys with InjectionKey<T> so injections are unique and typed.

BAD:

export default {
  install(app) {
    app.provide('http', axios)
    app.provide('config', appConfig)
  }
}

GOOD:

import type { InjectionKey } from 'vue'
import type { AxiosInstance } from 'axios'

interface AppConfig {
  apiUrl: string
  timeout: number
}

export const httpKey: InjectionKey<AxiosInstance> = Symbol('http')
export const configKey: InjectionKey<AppConfig> = Symbol('appConfig')

export default {
  install(app) {
    app.provide(httpKey, axios)
    app.provide(configKey, { apiUrl: '/api', timeout: 5000 })
  }
}

Provide Required Injection Helpers

Wrap required injections in composables that throw clear setup errors.

import { inject } from 'vue'
import { authKey, type AuthService } from '@/injection-keys'

export function useAuth(): AuthService {
  const auth = inject(authKey)
  if (!auth) {
    throw new Error('Auth plugin not installed. Did you forget app.use(authPlugin)?')
  }
  return auth
}