What is it called and how to implement it?

Question

Web development

These gray bars are displayed before the data is uploaded or how it is uploaded. How to implement it?

If there is a React way, please post some links.

Answer 1

https://zalog.ro/placeholder-loading/
https://github.com/danilowoz/react-content-loader/

Answer 2

I've been scratching my head all the time how to google it))