from unix timestamp to datetime

Without moment.js:

var time_to_show = 1509968436; // unix timestamp in seconds

var t = new Date(time_to_show * 1000);
var formatted = ('0' + t.getHours()).slice(-2) + ':' + ('0' + t.getMinutes()).slice(-2);

document.write(formatted);

Note my use of t.format comes from using Moment.js, it is not part of JavaScript's standard Date prototype.

A Unix timestamp is the number of seconds since 1970-01-01 00:00:00 UTC.

The presence of the +0200 means the numeric string is not a Unix timestamp as it contains timezone adjustment information. You need to handle that separately.

If your timestamp string is in milliseconds, then you can use the milliseconds constructor and Moment.js to format the date into a string:

var t = new Date( 1370001284000 );
var formatted = moment(t).format("dd.mm.yyyy hh:MM:ss");

If your timestamp string is in seconds, then use setSeconds:

var t = new Date();
t.setSeconds( 1370001284 );
var formatted = moment(t).format("dd.mm.yyyy hh:MM:ss");

Looks like you might want the ISO format so that you can retain the timezone.

var dateTime = new Date(1370001284000);
dateTime.toISOString(); // Returns "2013-05-31T11:54:44.000Z"

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date/toISOString