fast-track.js

// http://reaktor.fi/ura/fast_track/

function find(input) {

  'use strict';

  function toInt(s) {
    return parseInt(s, 10);
  }

  function product(a, b) {
    return a * b;
  }

  return _.range(0, input.length - 5)
          .map(function (i) {
            return input.slice(i, i + 5);
          }).reduce(function (acc, curr) {
            return Math.max(acc, curr.split('').map(toInt).reduce(product));
          }, -1);
}