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Documentation Index

Fetch the complete documentation index at: https://extension.js.org/llms.txt

Use this file to discover all available pages before exploring further.

Use special folders when your extension needs entrypoints or assets that do not fit cleanly in manifest.json. Handle extra pages, runtime-injected scripts, static assets with exact paths, and companion extensions for local development without splitting your project structure.

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Template examples

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special-folders-pages

special-folders-pages template screenshot See the pages/ special folder in action with extra HTML entrypoints. 
npx extension@latest create my-extension --template=special-folders-pages
Repository: extension-js/examples/special-folders-pages

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special-folders-scripts

special-folders-scripts template screenshot See the scripts/ special folder in action with standalone script entrypoints. 
npx extension@latest create my-extension --template=special-folders-scripts
Repository: extension-js/examples/special-folders-scripts

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Why this matters

The manifest does not directly declare many extension files. These include iframe pages, scripts you inject dynamically with chrome.scripting.executeScript, and static vendor assets. You may also need companion extensions during development. Special folders make all of these first-class in the build pipeline.

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How it works

Each special folder has a specific role:
Folder nameDescription
pages/Adds HTML pages to compilation as entrypoints, even when the manifest does not list them.
scripts/Adds script files to compilation as entrypoints, even when no manifest or HTML entry references them.
public/Copies static assets to the output root as-is (public/** → dist/**) without bundling or transformation.
extensions/Provides a conventional location for load-only companion extensions in dev/preview/start workflows.

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pages/: additional HTML entrypoints

Use pages/ for extra extension pages such as sandbox iframes, diagnostics pages, or internal tools. Extension.js treats each .html file in pages/ as an entrypoint and compiles it like manifest-declared pages. For a sandboxed iframe example, see the Chrome Sandbox Sample.

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scripts/: standalone script entrypoints

Use scripts/ for executable scripts that you load dynamically and that do not tie to an HTML page entry. Extension.js compiles files in scripts/ as entrypoints using the same extension resolution pipeline as the rest of your project.

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Important contract

When you use a scripts/ entry as a content-script-like runtime entry, follow the content script initialization pattern. This is the default-export contract Extension.js expects for safe hot-reload of injected scripts:
  • Export a default function.
  • Perform setup inside that function.
  • Optionally return a synchronous cleanup.
This matters most during development, where Extension.js remounts content-script-like entries safely instead of using full page reloads.

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Node.js scripts are not allowed in scripts/

Extension.js wraps every file inside scripts/ with a browser content-script mount runtime. If you place a Node.js-only file there (for example, a CLI launcher or build helper), the wrapper breaks the file. The shebang is no longer on line 1, and Node-only APIs are unavailable in the browser context. Extension.js detects two Node.js indicators and throws an error at build time:
  • A shebang (#!/usr/bin/env node) on line 1.
  • An import from the node: protocol (for example, import fs from 'node:fs').
If you see scripts/ is a reserved folder in Extension.js, move the file to a different folder at the project root, for example, bin/, tools/, ops/, tasks/, or ci-scripts/.
For dynamic injection examples, see the Chrome Scripting Sample.

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public/: copy-only static assets

Use public/ when you need stable file paths and no bundling/transformation. Extension.js copies everything under public/ to the output root 1:1.

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Important public/ guard

Do not place manifest.json at public/manifest.json. Extension.js prevents this to avoid overwriting the generated manifest during compilation.

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extensions/: companion extensions (load-only)

When you use companion extensions (for example, DevTools helpers), Extension.js supports an extensions/ folder as a load-only source in dev/preview/start flows. At a high level:
  • Scans subfolders under extensions/ for unpacked extension roots (manifest.json present).
  • Extension.js loads companion extensions alongside your main extension.
  • Use this folder to load companion extensions, not to build them into your main artifact.
You can also load companion extensions via the --extensions CLI flag or the extensions key in extension.config.js: 
# Load from a local folder
extension dev --extensions ./path/to/companion

# Load from Chrome Web Store or Firefox Add-ons
extension dev --extensions "https://chromewebstore.google.com/detail/react-developer-tools/fmkadmapgofadopljbjfkapdkoienihi"
Extension.js automatically downloads, unpacks, and loads store URLs alongside your extension.

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Development behavior (watch mode)

In development watch mode, Extension.js monitors pages/ and scripts/ for file set changes:
  • Adding supported files triggers a warning (you can keep working).
  • Removing a supported file triggers a compilation error. Restart the dev server to recover.
This protects the running compilation graph from stale or broken entrypoints.

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Best practices

  • Keep shared runtime assets in public/: Use it for files that must keep exact names and paths in output.
  • Use pages/ and scripts/ for true entrypoints: Keep off-manifest execution paths explicit.
  • Restart dev server after entrypoint changes: Especially after removing files under pages/ or scripts/.
  • Keep companion extensions isolated: Treat extensions/ as load-only dependencies for local workflows.
  • Do not place manifest.json in public/: Extension.js blocks public/manifest.json to protect the generated extension output.

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Next steps