Learn Javascript online

HTML tutorial
https://www.w3schools.com/html/default.asp

Web development tutorials
https://developer.mozilla.org/en-US/docs/Learn

Here are some sites to learn javascript online

Online Javascript editor
https://js.do/

Online javascript development and testing
https://jsfiddle.net/
https://www.webtoolkitonline.com/javascript-tester.html

Javascript tutorial
https://www.w3schools.com/js/