Currying

A function such as add(x, y) takes all of its arguments in one call. The same work can be split into a chain of functions that each take one argument: the first call receives x and returns a function, and the second call receives y and returns the result. Turning a function of several arguments into such a chain of one-argument functions is called currying, after the logician Haskell Curry.

From add(x, y) to add(x)(y)

The curried version of a two-argument function is a function that returns another function.

function curriedFunction(a) {