Moment.js

One of my least favorite parts of coding is working with timezones, date/time formatting and localization... Momentjs solves all this and more. One of my favorite features is its inbuilt "humanization" of duration (and customizable thresholds) like "a day ago" or "in 5 minutes." It has powerful parsing, amazing abbreviation support and awesome locales. I could not recommend this more.

I'm surprised this library just got featured. It's been one of my favorites libraries for a long while.

Best javascript library for manipulating dates hands down.