lodash factorial

factorial.js

// Imperetive:
function factorial(n) {
  var result = 1;
  for (var i = 1; i <= n; i++) {
    result *= i 
  }
  return result;
}


// Functional:
// (creates the array then reduces it)
function factorial(n) {
  return _.range(1, n+1)
    .reduce(function(p,i) { 
      return p*i;
    });
}

// Functional Better:
// (array creation and reduction done in one pass)
function factorial(n) {
  return _(_.range(1, n+1)).
    .reduce(function(p,i) {return p*i})
    .value();
}