Vite Plugin Development

Use when developing Vite plugins: scaffolding plugin structure, implementing hooks (transform, resolveId, load, buildStart, etc.), handling virtual modules, HMR integration, SSR compatibility, and publishing to npm. Covers Vite 5/6 plugin API.

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

Hook	Phase	Purpose
config	Both	Modify resolved config
configResolved	Both	Read final config
buildStart	Both	Initialize plugin state
resolveId	Both	Custom module resolution
load	Both	Custom module content
transform	Both	Code transformation
generateBundle	Build	Post-process output
configureServer	Serve	Extend dev server
handleHotUpdate	Serve	Custom HMR logic

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)