var d = Date.parse("Fri, 4 Dec 2008 15:13:00 +0000");
var dateFunc = new Date();
var timeSince = dateFunc.getTime() - d;
var inSeconds = timeSince / 1000;
var inMinutes = timeSince / 1000 / 60;
var inHours = timeSince / 1000 / 60 / 60;
var inDays = timeSince / 1000 / 60 / 60 / 24;
var inYears = timeSince / 1000 / 60 / 60 / 24 / 365;

// in seconds
if(Math.round(inSeconds) == 1){
document.write("1 second ago");
}
else if(inMinutes < 1.01){
document.write(Math.round(inSeconds) + " seconds ago");
}

// in minutes
else if(Math.round(inMinutes) == 1){
document.write("1 minute ago");
}
else if(inHours < 1.01){
document.write(Math.round(inMinutes) + " minutes ago");
}

// in hours
else if(Math.round(inHours) == 1){
document.write("1 hour ago");
}
else if(inDays < 1.01){
document.write(Math.round(inHours) + " hours ago");
}

// in days
else if(Math.round(inDays) == 1){
document.write("1 day ago");
}
else if(inYears < 1.01){
document.write(Math.round(inDays) + " days ago");
}

// in years
else if(Math.round(inYears) == 1){
document.write("1 year ago");
}
else
{
document.write(Math.round(inYears) + " years ago");
}

This takes a very readable date, such as "Fri, 4 Dec 2008 15:13:00 +0000", and outputs it as a relative date (such as "1 hour ago").

Javascript parse relative date

javascript, date

JavaScript