Calculate the number of leading zeroes in n!

leading-zeroes-in-factorial-of-n.js

function range(first, last) {
 const length = last - first + 1
 return new Array(length).fill(-1, 0, length).map(function(v, i) { return i + first; })
}

function factZeros(n) {
 return range(1, Math.floor(Math.log(n) / Math.log(5))).map(x => Math.pow(5, x)).map(x => Math.floor(n / x)).reduce((acc, curr) => acc + curr, 0)
}