The World Wide Web Consortium (W3C) is an international community where Member organizations, a full-time staff, and the public work together to develop Web standards.
w3.org/WAI
Accessibility resources free online from the international standards organization: W3C Web Accessibility Initiative (WAI).
html.spec.whatwg.org
An understanding of Web IDL, HTTP, XML, Unicode, character encodings, JavaScript, and CSS will also be helpful in places but is not essential.
standardjs.com
JavaScript Style Guide, with linter & automatic code fixer.