extension.js is a zero-configuration command-line interface (CLI) and development toolkit designed for creating, developing, and building cross-browser web extensions. It streamlines the development workflow by providing integrated tools for producing extensions compatible with major browsers including Chrome, Edge, Firefox, and Safari, all without requiring complex or manual build configurations. The package is currently stable at version 3.13.5 (as of April 11, 2026) and demonstrates a rapid release cadence with frequent patches and minor versions, highlighting active maintenance and quick turnaround on bug fixes and features. Its key differentiators include a 'zero-config' philosophy, native TypeScript support, and first-class integration with popular frameworks like React, aiming to significantly reduce setup overhead for developers targeting diverse browser environments. Beyond its CLI, extension.js also offers a programmatic API for `create` and `develop` operations, enabling custom build pipeline integration.
npm install extensionVerified import paths — ran on the pinned version, not inferred.
This quickstart demonstrates how to programmatically create a new React TypeScript extension project and then launch its development server, automatically opening it in a Chromium browser with live reloading enabled.
Remove any usage of the `extensionStart` option from your `develop` calls. The `develop` function will now handle the entire lifecycle.
Upgrade your Node.js environment to version 18 or newer (e.g., using nvm, fnm, or directly installing).
Upgrade to version `3.13.5` or later. Alternatively, specify a static, non-zero port number using `--port <number>`.
Upgrade to version `3.13.4` or later to benefit from improved dependency resolution logic.
Upgrade to version `3.13.4` or later to ensure the `--install` flag is correctly honored.
Upgrade to version `3.12.0` or later to mitigate the Preact VNode injection vulnerability.
Upgrade to version `3.14.0-next.0` or later to receive the fix for the `follow-redirects` auth header leak vulnerability.
Update your Node.js environment to version 18 or newer. Use `nvm install 18` or similar version manager commands, then `nvm use 18`.
Remove the `extensionStart` option from your `develop` function calls. The function now orchestrates the full build and preview process.
Upgrade `extension` to version `3.13.5` or newer. Alternatively, specify a different, non-zero port number.
Upgrade `extension` to version `3.13.4` or newer to fix project dependency resolution issues.
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