Unfortunately, the language has changed so much in recent years that I wouldn’t necessarily recommend that book anymore. A large number of fundamental features have been introduced since 2008, including async/await, lambda functions, class and extends syntax, proxies, and a ton of builtin methods like map() and forEach() on native list types.

For sure, these were the old days before jQuery was even considered a standard library. It was still duking it out with YUI and Prototype.

I'm fairly sure Lambda functions have always been part of javascript?

Anonymous functions indeed have. I think he means the arrow function syntax.

Yes, my bad. I meant arrow functions.

function () {}'s have been there forever, but () => {}'s have different semantics and are somewhat new