Multi line anonymous functions. An anonymous function is just as good as a true function in JavaScript.

Lambdas are incredibly limited and encourage the declaration of a whole separate function that now lives physically far from its use.

List comprehensions are also really underpowered and I personally hate the map and filter functions and their goofy list-like types.

Check out linq in .net, streams in Java, array in JS, collections in scala to see the expressive power of a fluent interface on collections