Vite Plugin Development

When to Use

• Building a custom Vite plugin from scratch
• Implementing transform/resolve hooks for special file types
• Creating virtual modules or runtime injections
• Adding HMR (Hot Module Replacement) support
• Making plugins SSR-compatible
• Publishing a plugin package to npm

Core Workflow

1. Plugin Scaffold

Every Vite plugin is a factory function returning a plugin object:

import type { Plugin } from 'vite'

export interface MyPluginOptions {
  include?: string | RegExp | (string | RegExp)[]
  exclude?: string | RegExp | (string | RegExp)[]
}

export default function myPlugin(options: MyPluginOptions = {}): Plugin {
  return {
    name: 'vite-plugin-my',          // required, unique name
    enforce: 'pre',                   // 'pre' | 'post' | undefined
    apply: 'build',                   // 'build' | 'serve' | ((config, env) => bool)

    // lifecycle hooks below...
  }
}

2. Key Hooks

3. Transform Hook Pattern

transform(code, id) {
  if (!id.endsWith('.myext')) return null  // return null = skip
  const transformed = doTransform(code)
  return {
    code: transformed,
    map: null,  // provide sourcemap when possible
  }
},

4. Virtual Modules

const VIRTUAL_ID = 'virtual:my-module'
const RESOLVED_ID = '\0' + VIRTUAL_ID   // prefix \0 to avoid collisions

resolveId(id) {
  if (id === VIRTUAL_ID) return RESOLVED_ID
},
load(id) {
  if (id === RESOLVED_ID) {
    return `export const data = ${JSON.stringify(myData)}`
  }
},

5. HMR Support

handleHotUpdate({ file, server }) {
  if (file.endsWith('.myext')) {
    server.ws.send({ type: 'full-reload' })
    return []  // prevent default HMR
  }
},

6. SSR Compatibility Checklist

• Check options.ssr in transform / load hooks
• Avoid browser-only APIs at transform time
• Mark side-effect-free modules: set moduleSideEffects: false
• Test with vite build --ssr

7. Testing Strategy

// Use vite's createServer for integration tests
import { createServer } from 'vite'
const server = await createServer({ plugins: [myPlugin()] })
const mod = await server.ssrLoadModule('/src/test.myext')

Publishing Checklist

• package.json main + module + types fields set
• peerDependencies: "vite": "^5.0.0 || ^6.0.0"
• README with usage example + options table
• Export TypeScript types
• Test against Vite 5 and 6
• vite-plugin- prefix in package name (ecosystem convention)