Ответ 1
var timestamp = 1293683278;
var date = new Date(timestamp*1000);
var year = date.getFullYear();
var month = date.getMonth() + 1;
var day = date.getDate();
var hours = date.getHours();
var minutes = date.getMinutes();
var seconds = date.getSeconds();
alert(year + "-" + month + "-" + day + " " + hours + ":" + minutes + ":" + seconds);
Подробнее см. js Date docs.
Другой способ:
var timestamp = 1293683278;
var date = new Date(timestamp*1000);
var iso = date.toISOString().match(/(\d{4}\-\d{2}\-\d{2})T(\d{2}:\d{2}:\d{2})/)
alert(iso[1] + ' ' + iso[2]);