Parsing a date string and adding a week
var d = new Date(Date.parse("15/04/2009")); d = d.setDate(d.getDate() + 7);
The above code is painful and unintuitive.
The above can be written like:
var d = Date.parse("15/04/2009").next().week();
var d = Date.parse("15/04/2009").add(1).week();
Basically it simplifies working with dates on the client site and the feature I found most useful was being about to tell what day of the week it is:
var isWednesday = Date.parse("15/04/2009").is().Wednesday();