Mastering JavaScript Functional Programming

Summing an array

The most common example of application of .reduce(), usually seen in all textbooks and web pages, is summing all the elements of an array. So, in order to keep with tradition, let's start with precisely that example!

Basically, to reduce an array you must provide a dyadic function (that is, a function with two parameters; binary would be an another name for that) and an initial value. In our case, the function will sum its two arguments. Initially, the function will be applied to the provided initial value and the first element of the array, so for us the first result we have to provide is a zero, and the first result will be the first element itself. Then, the function will be applied again, this time to the result of the ...