How to add region in java script file, visual studio

It depends only on the IDE.

vscode, for example, added support for code regions in september 2017

https://code.visualstudio.com/updates/v1_17#_folding-regions

For javascript:

//#region

code

//#endregion

or

//region

and

//endregion

The same syntax could work also in different IDEs.