A solution to this code challenge: https://www.interviewcake.com/question/javascript/cake-thief

cakeThief.js

class Bag {  
  constructor (capacity) {
    this.capacity = capacity;
    this.cakes = [];
    this.weight = 0;
    this.value = 0;
  }

  addCake (cake) {
    this.cakes.push(cake);
    this.value += cake.value;
    this.weight += cake.weight;
  }

  getCapacityRemaining () {
    return this.capacity - this.getWeight();
  }

  getValue () {
    return this.value;
  }

  getWeight () {
    return this.weight;
  }
}

let cakeTypes = [
  {weight: 7, value: 160},
  {weight: 3, value: 90},
  {weight: 1, value: 15}
];

// maxDuffelBagValue(cakeTypes, 20);

function maxDuffelBagValue (cakeTypes, capacity) {
  let bag = new Bag(capacity),
      // clean our cake types to cover out of bounds values
      validCakeTypes = cleanCakeTypes(cakeTypes),
      // figure out what the smallest cake is
      smallestCake = getSmallestCakeType(validCakeTypes);

  // until we don't have enough weight left, find the most valuable cake
  for (var capacityLeft = capacity; capacityLeft >= smallestCake.weight; capacityLeft = bag.getCapacityRemaining()) {
    // reduce our cakeTypes to the index of the highest value density that can fit
    let bestCake = validCakeTypes.reduce((prev, next) => {
      // make sure this next cake will fit
      if (next.weight <= capacityLeft) {
        // decide which is higher value-weight ratio
        return prev.value / prev.weight > next.value / next.weight ? prev : next;
      }
      // this next cake doesn't fit, keep the previous
      else return prev;
    }, {value: 0, weight: 1});

    // add the cake to our bag (adding to its weight and value)
    bag.addCake(bestCake);
  }

  return bag.getValue();
}

/**
 * reduce our cakeType collection down to one with the lowest weight
 * @param {array} cakeTypes - collection of cakeType object {weight, value}
 * @return {object} cakeType
*/
function getSmallestCakeType (cakeTypes) {
  return cakeTypes.reduce((prev, next) => prev.weight < next.weight ? prev : next);
}

/**
 * cleanCakeTypes - filters out invalid cakeTypes
 * @param {array} cakeTypes - collection of cakeType object {weight, value}
 * @return {array} filtered collection of cakeType objects
 */
function cleanCakeTypes (cakeTypes) {
  // filter out any cake types with weight or value of 0, that's unreal!
  return cakeTypes.filter((type) => type.weight > 0 && type.value > 0);
}