Adding Glean to your JavaScript project

This page provides a step-by-step guide on how to integrate the Glean.js library into a JavaScript project.

Nevertheless this is just one of the required steps for integrating Glean successfully into a project. Check you the full Glean integration checklist for a comprehensive list of all the steps involved in doing so.

Currently, these bindings support collecting data from Browser Extensions (cross-browser) and Qt/QML applications.


  • Node.js >= 12.20.0
  • npm >= 7.0.0
  • Webpack >= 5.34.0
  • Python >= 3.6
    • The glean command requires Python to download glean_parser which is a Python library

Browser extension specific requirements

  • webextension-polyfill >= 0.8.0
    • Glean.js assumes a Promise-based browser API: Firefox provides such an API by default. Other browsers may require using a polyfill library such us webextension-polyfill when using Glean in browser extensions
  • Host permissions to the telemetry server
    • Only necessary if the defined server endpoint denies cross-origin requests
    • The default server does require this type of permission. Follow Bug 1676676 for updates on this requirement
  • "storage" API permissions

Browser extension example configuration

The manifest.json file of the sample browser extension available on the mozilla/glean.js repository provides an example on how to define the above permissions as well as how and where to load the webextension-polyfill script.

Setting up the dependency

The Glean.js package is distributed as an npm package @mozilla/glean.

Install Glean.js in your JavaScript project, by running:

npm install @mozilla/glean

Then import Glean into your project:

// Glean.js for webextensions
// esm
import Glean from "@mozilla/glean/webext";
// cjs
const { default: Glean } = require("@mozilla/glean/webext");

The currently available entry points are:

  • @mozilla/glean/webext

Security considerations

In case of privilege-escalation attack into the context of the web extension using Glean, the malicious scripts would be able to call Glean APIs or use the APIs directly. That would be a risk to Glean data, but not caused by Glean. Glean-using extensions should be careful not to relax the default Content-Security-Policy that generally prevents these attacks.

Common import errors

"Cannot find module '@mozilla/glean'"

Glean.js does not have a main package entry point. Instead it relies on a series of entry points depending on the platform you are targeting.

In order to import Glean use:

import Glean from '@mozilla/glean/{your-platform}'

"Module not found: Error: Can't resolve '@mozilla/glean/webext' in '...'"

Glean.js relies on Node.js' subpath exports feature to define multiple package entry points.

Please make sure that you are using a supported Node.js runtime and also make sure the tools you are using support this Node.js feature.

Setting up metrics and pings code generation

In JavaScript, the metrics and pings definitions must be parsed at build time. The @mozilla/glean package exposes glean_parser through the glean script.

To parse your YAML registry files using this script, define a new script in your package.json file:

  // ...
  "scripts": {
    // ...
    "build:glean": "glean translate path/to/metrics.yaml path/to/pings.yaml -f javascript -o path/to/generated",
    // Or, if you are building for a Typescript project
    "build:glean": "glean translate path/to/metrics.yaml path/to/pings.yaml -f typescript -o path/to/generated"

Then run this script by calling:

npm run build:glean

Automation steps


Prefer using the Glean Dictionary

While it is still possible to generate Markdown documentation, if working on a public Mozilla project rely on the Glean Dictionary for documentation. Your product will be automatically indexed by the Glean Dictionary after it gets enabled in the pipeline.

One of the commands provided by glean_parser allows users to generate Markdown documentation based on the contents of their YAML registry files. To perform that translation, use the translate command with a different output format, as shown below.

In your package.json, define the following script:

  // ...
  "scripts": {
    // ...
    "docs:glean": "glean translate path/to/metrics.yaml path/to/pings.yaml -f markdown -o path/to/docs",

Then run this script by calling:

npm run docs:glean

YAML registry files linting

Glean includes a "linter" for the YAML registry files called the glinter that catches a number of common mistakes in these files. To run the linter use the glinter command.

In your package.json, define the following script:

  // ...
  "scripts": {
    // ...
    "lint:glean": "glean glinter path/to/metrics.yaml path/to/pings.yaml",

Then run this script by calling:

npm run lint:glean