Javascript: output current datetime in YYYY/mm/dd hh:m:sec format

You can build it manually:

var m = new Date();
var dateString = m.getUTCFullYear() +"/"+ (m.getUTCMonth()+1) +"/"+ m.getUTCDate() + " " + m.getUTCHours() + ":" + m.getUTCMinutes() + ":" + m.getUTCSeconds();

and to force two digits on the values that require it, you can use something like this:

("0000" + 5).slice(-2)

Which would look like this:

var m = new Date();
var dateString =
    m.getUTCFullYear() + "/" +
    ("0" + (m.getUTCMonth()+1)).slice(-2) + "/" +
    ("0" + m.getUTCDate()).slice(-2) + " " +
    ("0" + m.getUTCHours()).slice(-2) + ":" +
    ("0" + m.getUTCMinutes()).slice(-2) + ":" +
    ("0" + m.getUTCSeconds()).slice(-2);

console.log(dateString);

No library, one line, properly padded

const str = (new Date()).toISOString().slice(0, 19).replace(/-/g, "/").replace("T", " ");

It uses the built-in function Date.toISOString(), chops off the ms, replaces the hyphens with slashes, and replaces the T with a space to go from say '2019-01-05T09:01:07.123' to '2019/01/05 09:01:07'.

Local time instead of UTC

const now = new Date();
const offsetMs = now.getTimezoneOffset() * 60 * 1000;
const dateLocal = new Date(now.getTime() - offsetMs);
const str = dateLocal.toISOString().slice(0, 19).replace(/-/g, "/").replace("T", " ");

With jQuery date format :

$.format.date(new Date(), 'yyyy/MM/dd HH:mm:ss');

https://github.com/phstc/jquery-dateFormat

Enjoy