x2js - XML to JSON and back for JavaScript
JavaScript happiness style linter
XRegExp provides augmented (and extensible) JavaScript regular expressions. You get modern syntax and flags beyond what browsers support natively. XRegExp is also a regex utility belt with tools to make your grepping and parsing easier, while freeing you from regex cross-browser inconsistencies and other annoyances.
State machines and statecharts for the modern web.
Xterm.js is a front-end component written in TypeScript that lets applications bring fully-featured terminals to their users in the browser.