Skilldrick » Easy functional programming in JavaScript with Underscore.js — part 1: "Functional programming (FP) is all about the idea of functions as a mapping from one value to another. An FP function just turns one value into another – it doesn’t have side effects. Side effects are anything that happens within the function that changes something outside of the function. For example, changing the value of a variable not defined in the function, or logging output, or showing an alert message … basically anything that happens in the function. The only thing an FP function does is takes in a value, and returns a new value.
Another interesting thing about FP is the use of higher-order functions. These are functions that either take or return functions as values (or both). I’m mainly going to be looking at functions that take other functions as parameters, because there are some interesting things you can do with that."
