I am using following approach:
var myVar=setInterval(function(){myDateTimer()},60000);
function makeArray()
{
for (i = 0; i<makeArray.arguments.length; i++)
this[i + 1] = makeArray.arguments[i];
}
function myDateTimer()
{
var months = new makeArray('January','February','March','April','May',
'June','July','August','September','October','November','December');
var days = ['Sunday','Monday','Tuesday','Wednesday','Thursday','Friday','Saturday'];
var date = new Date();
var day = date.getDate();
var month = date.getMonth() + 1;
var yy = date.getYear();
var year = (yy < 1000) ? yy + 1900 : yy;
var hours = date.getHours();
var minutes = date.getMinutes();
var finaldate = days[ date.getDay() ] + ", " + months[month] + " " + day + ", " + year + " " + hours +" : " + minutes;
document.getElementById("showDateTime").innerHTML=finaldate;
}