jsは配列の中で3つの数の最大積を求めます.

// An highlighted block
function maxThreeSum (array) {
   var sort_array = array.sort((a, b)=>(a - b)),
         product1 = 1,
         product2 = 1,
         sort_array_length = sort_array.length - 1;
         for(var i = sort_array_length; i > sort_array_length - 3; i--) {
             product1 = product1 * sort_array[i];
         }
         product2 = sort_array[0] * sort_array[1] * sort_array[sort_array_length];
         if (product1 > product2) return product1;
         return product2;
}

// An highlighted block
function maxThreeSum (sourceAry) {
   var [a, b, c, d, e] = [Infinity, Infinity, -Infinity, -Infinity, -Infinity];
   sourceAry.forEach(item => {
       if (item < a) {
           b = a;
           a = item;
       } else if (item < b) {
           b = item;
       }
       if (item > e) {
           c = d;
           d = e;
           e = item;
       } else if (item > d) {
           c = d;
           d = item;
       } else if (item > c) {
           c = item;
       }
   });
   return Math.max(a * b * e, c * d * e);
}