What is the optimal front-end internationalization model?

Question

JavaScript

The backend sends and receives data in a fixed system format. The frontend accordingly displays and receives data from the user in the same format at the moment.
Design generally speaking under {Custom| bootstrap | jquery}.
What is the optimal model and set of libraries for formatting input and output on the frontend, based on the user's TimeZone, interface language, and the selected formats at the request of the user?
ps field types Number,Date,DateTime,Time

Answer 1

and use the current locale of the browser, so changing the output format directly will not work: stackoverflow.com/questions/2968817/is-there-a-way...
value these controls always accept in ISO format