Mastering JavaScript Functional Programming - Second Edition

Summing an array

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

Basically, to reduce an array, you must provide a dyadic function (that is, a function with two parameters; binary would be 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 ...