Mastering JavaScript Functional Programming

Composing

Composing is quite similar to pipelining, but has its roots in mathematical theory. The concept of composition is simple - a sequence of function calls, in which the output of one function is the input for the next one - but the order is reversed from the one in pipelining. In the latter, the first function to be applied is the leftmost one, but in composition, you start with the rightmost one. Let's investigate this a bit more.

When you define the composition of, say, three functions, as (f∘ g∘ h) and apply it to x, this is equivalent to what you would write as f(g(h(x))). It's important to note that, as with pipelining, the arity of the first function to be applied can be anything, but all the other functions must be unary. Also, ...