how to play audio only with YouTube in Chrome and iOS

Author: Asrman

 1) Chrome: https://chrome.google.com/webstore/detail/audio-only-youtube/pkocpiliahoaohbolmkelakpiphnllog?hl=en 

2) iOS:   You can download Youtube Music, then: account->Settings->Playback & restrictions - > Don't play music videos (check)