moment.js
is great but sometimes you don't want to pull a large number of dependencies for simple things.
The following works as well:
var tzoffset = (new Date()).getTimezoneOffset() * 60000; //offset in milliseconds
var localISOTime = (new Date(Date.now() - tzoffset)).toISOString().slice(0, -1);
// => '2015-01-26T06:40:36.181'
The slice(0, -1)
gets rid of the trailing Z
which represents Zulu timezone and can be replaced by your own.