Display date from JS

i have some js code wich take data  from SYSATTACHMENTS table, sysmodtime field.

Vvariable is assigned the value like:

 

...
var FileDate = attach.sysmodtime;
...

 

Then i display this FileDate on form (configurationItem.g) and this looks like that:

Thu Feb 09 2017 11:32:06 GMT 0300

How can i change display format to set it like i need, for example:

2017/02/09 11:32:06

or

2017.02.09 11:32:06

...