Build and SSR

Library Mode

Build a library for distribution:

// vite.config.ts
import { resolve } from 'node:path'
import { defineConfig } from 'vite'

export default defineConfig({
  build: {
    lib: {
      entry: resolve(import.meta.dirname, 'lib/main.ts'),
      name: 'MyLib',
      fileName: 'my-lib',
    },
    rolldownOptions: {
      external: ['vue', 'react'],
      output: {
        globals: {
          vue: 'Vue',
          react: 'React',
        },
      },
    },
  },
})

Multiple Entries

build: {
  lib: {
    entry: {
      'my-lib': resolve(import.meta.dirname, 'lib/main.ts'),
      secondary: resolve(import.meta.dirname, 'lib/secondary.ts'),
    },
    name: 'MyLib',
  },
}

Output Formats

Single entry: es and umd
Multiple entries: es and cjs

Package.json Setup

{
  "name": "my-lib",
  "type": "module",
  "files": ["dist"],
  "main": "./dist/my-lib.umd.cjs",
  "module": "./dist/my-lib.js",
  "exports": {
    ".": {
      "import": "./dist/my-lib.js",
      "require": "./dist/my-lib.umd.cjs"
    },
    "./style.css": "./dist/my-lib.css"
  }
}

Multi-Page App

export default defineConfig({
  build: {
    rolldownOptions: {
      input: {
        main: resolve(import.meta.dirname, 'index.html'),
        nested: resolve(import.meta.dirname, 'nested/index.html'),
      },
    },
  },
})

SSR Development

Middleware Mode

Use Vite as middleware in a custom server:

import express from 'express'
import { createServer as createViteServer } from 'vite'

const app = express()

const vite = await createViteServer({
  server: { middlewareMode: true },
  appType: 'custom',
})

app.use(vite.middlewares)

app.use('*all', async (req, res, next) => {
  const url = req.originalUrl

  // 1. Read and transform index.html
  let template = await fs.readFile('index.html', 'utf-8')
  template = await vite.transformIndexHtml(url, template)

  // 2. Load server entry
  const { render } = await vite.ssrLoadModule('/src/entry-server.ts')

  // 3. Render app
  const appHtml = await render(url)

  // 4. Inject into template
  const html = template.replace('<!--ssr-outlet-->', appHtml)

  res.status(200).set({ 'Content-Type': 'text/html' }).end(html)
})

app.listen(5173)

SSR Build

{
  "scripts": {
    "build:client": "vite build --outDir dist/client",
    "build:server": "vite build --outDir dist/server --ssr src/entry-server.ts"
  }
}

The --ssr flag:

Externalizes dependencies by default
Outputs for Node.js consumption

SSR Manifest

Generate asset mapping for preload hints:

vite build --outDir dist/client --ssrManifest

Creates dist/client/.vite/ssr-manifest.json mapping module IDs to chunks.

SSR Externals

Control which deps get bundled vs externalized:

export default defineConfig({
  ssr: {
    noExternal: ['some-package'],  // Bundle this dep
    external: ['another-package'], // Externalize this dep
  },
})

Conditional Logic

if (import.meta.env.SSR) {
  // Server-only code (tree-shaken from client)
}

JavaScript API

createServer

import { createServer } from 'vite'

const server = await createServer({
  configFile: false,
  root: import.meta.dirname,
  server: { port: 1337 },
})

await server.listen()
server.printUrls()

build

import { build } from 'vite'

await build({
  root: './project',
  build: { outDir: 'dist' },
})

preview

import { preview } from 'vite'

const previewServer = await preview({
  preview: { port: 8080, open: true },
})
previewServer.printUrls()

resolveConfig

import { resolveConfig } from 'vite'

const config = await resolveConfig({}, 'build')

loadEnv

import { loadEnv } from 'vite'

const env = loadEnv('development', process.cwd(), '')
// Loads all env vars (empty prefix = no filtering)

vite-build-ssr

details