Js: how to see if the webpage isn't at the top

Question

well, i wanna make a "scroll to the top" button that appears at the bottom right of the page when the page isn't at the top....

and likely can you tell me how to see if a specific section, let's say div#about 's Y pos of 0, reaches the top of the screen

Answer 1

https://code.sololearn.com/WwocKTfMqNTQ/?ref=app

Answer 2

How about these?
https://stackoverflow.com/questions/8218159/javascript-check-if-page-is-at-the-top#8218205

Answer 3

https://code.sololearn.com/W8o3IijOKFac/?ref=app
https://code.sololearn.com/Ws1HO2U0A227/?ref=app