When an add-on is submitted to Firefox for validation, the add-ons linter checks its code and displays relevant errors, warnings, or friendly messages for the developer to review. JavaScript is constantly evolving, and when the linter lags behind the language, developers may see syntax errors for code that is generally considered acceptable. These errors block developers from getting their add-on signed or listed on addons.mozilla.org.
On July 2, the linter was updated from ESLint 5.16 to ESLint 7.3 for JavaScript validation. This upgrades linter support to most ECMAScript 2020 syntax, including features like optional chaining, BigInt, and dynamic imports. As a quick note, the linter is still slightly behind what Firefox allows. We will post again in this blog the next time we make an update.
Want to help us keep the linter up-to-date? We welcome code contributions and encourage developers to report bugs found in our validation process.