reaktor.js

function (input) {
  return _.reduce(input, function(memo,val) {    
    memo.nums.push(val); // enqueue the current iterated value
    
    if (memo.nums.length >= 5) {
      while (memo.nums.length > 5) // dequeue excessive items
        memo.nums.shift();
    
      var product = _.reduce(memo.nums, function(product, number) { return product * number; }, 1);
      memo.high = Math.max(product, memo.high);
    }    
    
    return memo; // important to return the memo object so it doesn't
    				 // get emptied while looping the material.
  }, { "nums": [], "high": 0 }).high;
}