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Note: Paramters in the bracket are always optional
Here is the detail of parameters:
timeValue :An integer representing the number of milliseconds since 1 January 1970, 00:00:00 UTC.
var dt = new Date( "Aug 28, 2008 23:30:00" );
dt.setTime( 5000000 );
document.write( dt );
This will produce following result :
Thu Jan 1 06:53:20 UTC+0530 1970
To understand it in better way you can Try it yourself.