Partial function application and currying

Many languages support optional arguments, but not in JavaScript. JavaScript uses a different pattern entirely that allows for any number of arguments to be passed to a function. This leaves the door open for some very interesting and unusual design patterns. Functions can be applied in part or in whole.

Partial application in JavaScript is the process of binding values to one or more arguments of a function that returns another function that accepts the remaining, unbound arguments. Similarly, currying is the process of transforming a function with many arguments into a function with one argument that returns another function that takes more arguments as needed.

The difference between the two may not be clear now, but it will be obvious in the end.