Good examples of functional programing include functions like .map(), .reduce(), and .forEach(). The Underscore.js library contains many useful functional utilities. For simplicity, we’ll be making use of Underscore.js in this book.
If you click something, you want something to happen instantly. That impatience has led to wonderful advancements in UI design, such as Google Instant and the ground‐ breaking address lookup on The Wilderness Downtown. (“The Wilderness Downtown” is an interactive short film by Chris Milk set to the Arcade Fire song, “We Used To Wait.”
It was built entirely with the latest open web technologies.) Such functionality is powered by Ajax calls that do their thing in the background without slowing down the UI.