Configuring Vite

When running vite from the command line, Vite will automatically try to resolve a config file named vite.config.js inside project root (other JS and TS extensions are also supported).

The most basic config file looks like this:

export default {
  // config options
}

Note that to use ES modules syntax in the config file, it should be in a file detected as ESM by Node.js, e.g. .mjs or .js with "type": "module" in closest package.json.

You can also explicitly specify a config file to use with the --config CLI option (resolved relative to cwd):

bash

vite --config my-config.js

<ScrimbaLink href="https://scrimba.com/intro-to-vite-c03p6pbbdq/~05jg?via=vite" title="Configuring Vite">Watch an interactive lesson on Scrimba</ScrimbaLink>

::: tip CONFIG LOADING By default, Vite uses Rolldown to bundle the config into a temporary file and load it. If you're using an environment that supports TypeScript (e.g. Node 22.18+), or if you're only writing plain JavaScript, you can specify --configLoader native to use the environment's native runtime to load the config file. configLoader: 'native' is planned to become the default in a future major version. :::

Config Intellisense

Since Vite ships with TypeScript typings, you can leverage your IDE's intellisense with jsdoc type hints:

/** @type {import('vite').UserConfig} */
export default {
  // ...
}

Alternatively, you can use the defineConfig helper which should provide intellisense without the need for jsdoc annotations:

import { defineConfig } from 'vite'

export default defineConfig({
  // ...
})

Vite also supports TypeScript config files. You can use vite.config.ts with the defineConfig helper function above, or with the satisfies operator:

import type { UserConfig } from 'vite'

export default {
  // ...
} satisfies UserConfig

Conditional Config

If the config needs to conditionally determine options based on the command (serve or build), the mode being used, if it's an SSR build (isSsrBuild), or is previewing the build (isPreview), it can export a function instead:

import { defineConfig } from 'vite'
// ---cut---
export default defineConfig(({ command, mode, isSsrBuild, isPreview }) => {
  if (command === 'serve') {
    return {
      // dev specific config
    }
  } else {
    // command === 'build'
    return {
      // build specific config
    }
  }
})

It is important to note that in Vite's API the command value is serve during dev (in the cli vite, vite dev, and vite serve are aliases), and build when building for production (vite build).

isSsrBuild and isPreview are additional optional flags to differentiate the kind of build and serve commands respectively. Some tools that load the Vite config may not support these flags and will pass undefined instead. Hence, it's recommended to use explicit comparison against true and false.

Async Config

If the config needs to call async functions, it can export an async function instead. And this async function can also be passed through defineConfig for improved intellisense support:

import { defineConfig } from 'vite'
// ---cut---
export default defineConfig(async ({ command, mode }) => {
  const data = await asyncFunction()
  return {
    // vite config
  }
})

Using Environment Variables in Config

Environment variables available while the config itself is being evaluated are only those that already exist in the current process environment (process.env). Vite deliberately defers loading any .env* files until after the user config has been resolved because the set of files to load depends on config options like root and envDir, and also on the final mode.

This means: variables defined in .env, .env.local, .env.[mode], or .env.[mode].local are not automatically injected into process.env while your vite.config.* is running. They are automatically loaded later and exposed to application code via import.meta.env (with the default VITE_ prefix filter) exactly as documented in Env Variables and Modes. So if you only need to pass values from .env* files to the app, you don't need to call anything in the config.

If, however, values from .env* files must influence the config itself (for example to set server.port, conditionally enable plugins, or compute define replacements), you can load them manually using the exported loadEnv helper.

import { defineConfig, loadEnv } from 'vite'

export default defineConfig(({ mode }) => {
  // Load env file based on `mode` in the current working directory.
  // Set the third parameter to '' to load all env regardless of the
  // `VITE_` prefix.
  const env = loadEnv(mode, process.cwd(), '')
  return {
    define: {
      // Provide an explicit app-level constant derived from an env var.
      __APP_ENV__: JSON.stringify(env.APP_ENV),
    },
    // Example: use an env var to set the dev server port conditionally.
    server: {
      port: env.APP_PORT ? Number(env.APP_PORT) : 5173,
    },
  }
})

Debugging the Config File in VS Code

For the most reliable debugging experience, use the native config loader when starting Vite:

bash

vite --configLoader native

The native loader executes the original config file directly, so breakpoints in the config file and in plugin hooks such as transform map to the original source. It requires a runtime that supports the syntax used by your config file, such as Node.js 22.18+ for TypeScript files.

When using --configLoader bundle (the current default, though native is planned to become the default in a future major version), Vite generates an inline source map and writes the bundled config to node_modules/.vite-temp before loading it. If you need to use the bundle loader, add the temporary directory for the JavaScript Debug Terminal in .vscode/settings.json:

json

{
  "debug.javascript.terminalOptions": {
    "resolveSourceMapLocations": [
      "${workspaceFolder}/**",
      "!**/node_modules/**",
      "**/node_modules/.vite-temp/**"
    ]
  }
}

This setting only applies to the JavaScript Debug Terminal, it does not affect launch configurations started from the Run and Debug view. To support this for the Run and Debug view, add the temporary directory in .vscode/launch.json:

json

{
  "version": "0.2.0",
  "configurations": [
    {
      "type": "node",
      "request": "launch",
      "name": "Vite",
      "runtimeExecutable": "npm",
      "runtimeArgs": ["exec", "vite", "--configLoader", "bundle"],
      "console": "integratedTerminal",
      "sourceMaps": true,
      "resolveSourceMapLocations": [
        "${workspaceFolder}/**",
        "!**/node_modules/**",
        "**/node_modules/.vite-temp/**"
      ]
    }
  ]
}