Snowpack 3.0 Release Candidate is here! Read the announcement post →

snowpack.config.js 

// Example Configuration File
module.exports = {
  plugins: [
    /* ... */
  ],
  installOptions: {
    /* ... */
  },
  devOptions: {
    /* ... */
  },
  buildOptions: {
    /* ... */
  },
  proxy: {
    /* ... */
  },
  mount: {
    /* ... */
  },
  alias: {
    /* ... */
  },
};

config.installOptions

Settings that determine how Snowpack handles installing modules.

installOptions.dest string

  • Default:"web_modules"
  • Configure the install directory.

installOptions.sourceMap boolean

  • Emit source maps for installed packages.

installOptions.env {[ENV_NAME: string]: (string true)}

  • Sets a process.env. environment variable inside the installed dependencies. If set to true (ex: {NODE_ENV: true} or --env NODE_ENV) this will inherit from your current shell environment variable. Otherwise, set to a string (ex: {NODE_ENV: 'production'} or --env NODE_ENV=production) to set the exact value manually.

installOptions.treeshake boolean

  • Default:false, or true when run with snowpack build
  • Treeshake your dependencies to optimize your installed files. Snowpack will scan your application to detect which exact imports are used from each package, and then will remove any unused imports from the final install via dead-code elimination (aka tree shaking).

installOptions.installTypes boolean

  • Install TypeScript type declarations with your packages. Requires changes to your tsconfig.json to pick up these types.

installOptions.namedExports string[]

  • NOTE(v2.13.0): Snowpack now automatically supports named exports for most Common.js packages. This configuration remains for any package that Snowpack can’t handle automatically. In most cases, this should no longer be needed.
  • Import CJS packages using named exports (Example: import {useTable} from 'react-table').
  • Example: "namedExports": ["react-table"]

installOptions.externalPackage string[]

  • NOTE: This is an advanced feature, and may not do what you want! Bare imports are not supported in any major browser, so an ignored import will usually fail when sent directly to the browser.
  • Mark some imports as external. Snowpack won’t install them and will ignore them when resolving imports.
  • Example: "externalPackage": ["fs"]

installOptions.packageLookupFields string[]

  • Set custom lookup fields for dependency package.json file entrypoints, in addition to the defaults like “module”, “main”, etc. Useful for package ecosystems like Svelte where dependencies aren’t shipped as traditional JavaScript.
  • Example: "packageLookupFields": ["svelte"]

installOptions.rollup Object

  • Snowpack uses Rollup internally to install your packages. This rollup config option gives you deeper control over the internal rollup configuration that we use.

  • installOptions.rollup.plugins - Specify Custom Rollup plugins if you are dealing with non-standard files.

  • installOptions.rollup.dedupe - If needed, deduplicate multiple versions/copies of a packages to a single one. This helps prevent issues with some packages when multiple versions are installed from your node_modules tree. See rollup-plugin-node-resolve for more documentation.

  • installOptions.rollup.context - Specify top-level this value. Useful to silence install errors caused by legacy common.js packages that reference a top-level this variable, which does not exist in a pure ESM environment. Note that the 'THIS_IS_UNDEFINED' warning (“‘this’ keyword is equivalent to ‘undefined’ … and has been rewritten”) is silenced by default, unless --verbose is used.

installOptions.polyfillNode | boolean

If you depend on packages that depend on Node.js built-in modules ("fs", "path", "url", etc.) you can run Snowpack with --polyfill-node (or installOptions.polyfillNode: true in your config file). This will automatically polyfill any Node.js dependencies as much as possible for the browser. You can see the full list of supported polyfills here: https://github.com/ionic-team/rollup-plugin-node-polyfills

If you’d like to customize this polyfill behavior, skip the --polyfill-node flag and instead provide your own Rollup plugin for the installer:

// Example: If `--polyfill-node` doesn't support your use-case, you can provide your own custom Node.js polyfill behavior
module.exports = {
  installOptions: {
    polyfillNode: false,
    rollup: {
      plugins: [require('rollup-plugin-node-polyfills')({crypto: true, ...})],
    },
  },
};

config.devOptions

devOptions.port | number | Default: 8080

  • The port number to run the dev server on.

devOptions.fallback | string | Default: "index.html"

  • When using the Single-Page Application (SPA) pattern, this is the HTML “shell” file that gets served for every (non-resource) user route. Make sure that you configure your production servers to serve this as well.

devOptions.open | string | Default: "default"

  • Opens the dev server in a new browser tab. If Chrome is available on macOS, an attempt will be made to reuse an existing browser tab. Any installed browser may also be specified. E.g., “chrome”, “firefox”, “brave”. Set “none” to disable.

devOptions.output | "stream" | "dashboard" | Default: "dashboard"

  • Set the output mode of the dev console.
  • "dashboard" delivers an organized layout of console output and the logs of any connected tools. This is recommended for most users and results in the best logging experience.
  • "stream" is useful when Snowpack is run in parallel with other commands, where clearing the shell would clear important output of other commands running in the same shell.

devOptions.hostname | string | Default: localhost

  • The hostname where the browser tab will be open.

devOptions.hmr | boolean | Default: true

  • Toggles whether or not Snowpack dev server should have HMR enabled.

devOptions.hmrErrorOverlay | boolean | Default: true

  • When HMR is enabled, toggles whether or not a browser overlay should display javascript errors.

devOptions.secure | boolean

  • Toggles whether or not Snowpack dev server should use HTTPS with HTTP2 enabled.

devOptions.out | string | Default: "build"

  • NOTE: Deprecated, see buildOptions.out.
  • The local directory that we output your final build to.

config.buildOptions

buildOptions.out | string | Default: "build"

  • The local directory that we output your final build to.

buildOptions.baseUrl | string | Default: /

  • In your HTML, replace all instances of / with this (inspired by the same Create React App concept). This is useful if your app will be deployed to a subdirectory. Note: if you have homepage in your package.json, Snowpack will actually pick up on that, too.

buildOptions.clean | boolean | Default: false

  • Set to true if Snowpack should erase the build folder before each build.

buildOptions.metaDir | string | Default: __snowpack__

  • By default, Snowpack outputs Snowpack-related metadata such as HMR and ENV info to a folder called __snowpack__. You can rename that folder with this option (e.g.: metaDir: 'static/snowpack').

buildOptions.sourceMaps | boolean | Default: false

  • Experimental: Set to true to enable source maps

buildOptions.webModulesUrl | string | Default: web_modules

  • Rename your web modules directory.

config.testOptions

testOptions.files | string[] | Default: ["__tests__/**/*", "**/*.@(spec|test).*"]

  • The location of all test files.
  • All matching test files are scanned for installable dependencies during development, but excluded from both scanning and building in your final build.

config.proxy

If desired, "proxy" is where you configure the proxy behavior of your dev server. Define different paths that should be proxied, and where they should be proxied to.

The short form of a full URL string is enough for general use. For advanced configuration, you can use the object format to set all options supported by http-proxy.

This configuration has no effect on the final build.

Example:

// snowpack.config.json
{
  "proxy": {
    // Short form:
    "/api/01": "https://pokeapi.co/api/v2/",
    // Long form:
    "/api/02": {
      on: { proxyReq: (p, req, res) => /* Custom event handlers (JS only) */ },
      /* Custom http-proxy options */
    }
  }
}

Options:

  • "path".on | object (string: function)
    • on is a special Snowpack property for setting event handler functions on proxy server events. See the section on “Listening for Proxy Events” for a list of all supported events. You must be using a snowpack.config.js JavaScript configuration file to set this.
  • All options supported by http-proxy.

config.mount

mount: {
  [path: string]: string | {url: string, static: boolean, resolve: boolean}
}

The mount configuration lets you customize which directories should be included in your Snowpack build, and what URL they are mounted to. Given the following example configuration, you could expect the following results:

// Example: Basic "mount" usage
// snowpack.config.json
{
  "mount": {
    "src": "/_dist_",
    "public": "/"
  }
}
GET /src/a.js           -> 404 NOT FOUND ("./src" is mounted to "/_dist_/*", not "/src/*")
GET /_dist_/a.js        -> ./src/a.js
GET /_dist_/b/b.js      -> ./src/b/b.js
GET /public/robots.txt  -> 404 NOT FOUND ("./public" dir is mounted to "/*", not "/public/*")
GET /robots.txt         -> ./public/robots.txt

By default, Snowpack builds every mounted file by passing it through Snowpack’s build pipeline.

*New in Snowpack v2.15.0: You can customize the build behavior for a mounted directory using the expanded object notation:

  • url required: The URL to mount to, matching the simple form above.
  • static optional, default: false: If true, don’t build files in this directory and serve them directly to the browser.
  • resolve optional, default: true: If false, don’t resolve JS & CSS imports in your JS, CSS, and HTML files and send every import to the browser, as written. We recommend that you don’t disable this unless absolutely necessary, since it prevents Snowpack from handling your imports to things like packages, JSON files, CSS modules, and more.
// Example: Advanced "mount" usage
// snowpack.config.json
{
  "mount": {
    // Same behavior as the "src" example above:
    "src": {url: "/_dist_"},
    // Mount "public" to the root URL path ("/*") and serve files with zero transformations:
    "public": {url: "/", static: true, resolve: false}
  }
}

config.alias

object (package: package or path)

Note: In an older version of Snowpack, all mounted directories were also available as aliases by default. As of Snowpack 2.7, this is no longer the case and no aliases are defined by default.

The alias config option lets you define an import alias in your application. When aliasing a package, this allows you to import that package by another name in your application. This applies to imports inside of your dependencies as well, essentially replacing all references to the aliased package.

Aliasing a local directory (any path that starts with “./”) creates a shortcut to import that file or directory. While we don’t necessarily recommend this pattern, some projects do enjoy using these instead of relative paths:

-import '../../../../../Button.js';
+import '@app/Button.js';

Example:

// snowpack.config.json
{
  alias: {
    // Type 1: Package Import Alias
    "lodash": "lodash-es",
    "react": "preact/compat",
    // Type 2: Local Directory Import Alias (relative to cwd)
    "components": "./src/components"
    "@app": "./src"
  }
}

Environment Variables

// `import.meta.env` - Read process.env variables in your web app
fetch(`${import.meta.env.SNOWPACK_PUBLIC_API_URL}/users`).then(...)

// Supports destructuring as well:
const {SNOWPACK_PUBLIC_API_URL} = import.meta.env;
fetch(`${SNOWPACK_PUBLIC_API_URL}/users`).then(...)

// Instead of `import.meta.env.NODE_ENV` use `import.meta.env.MODE`
if (import.meta.env.MODE === 'development') {
  // ...

You can read environment variables directly in your web application via import.meta.env. If you’ve ever used process.env in Create React App or any Webpack application, this behaves exactly the same.

For your safety, Snowpack supports only environment variables which begin with SNOWPACK_PUBLIC_*. We do this because everything in your web application is sent to the browser, and we don’t want you to accidentally share sensitive keys/env variables with your public web application. Prefixing your frontend web env variables with SNOWPACK_PUBLIC_ is a good reminder that they will be shared with the world.

import.meta.env.MODE and import.meta.env.NODE_ENV are also both set to the current process.env.NODE_ENV value, so that you can change app behavior based on dev vs. build. The env value is set to development during snowpack dev and production during snowpack build. Use this in your application instead of process.env.NODE_ENV.

You can use environment variables in HTML files. All occurrences of %SNOWPACK_PUBLIC_*%, /, and production will be replaced at build time.

Remember: that these env variables are statically injected into your application for everyone at build time, and not runtime.