diff --git a/js-jest/src/gilded_rose.js b/js-jest/src/gilded_rose.js
index 48746965..bb0a71f3 100644
--- a/js-jest/src/gilded_rose.js
+++ b/js-jest/src/gilded_rose.js
@@ -1,67 +1,68 @@
 class Item {
-  constructor(name, sellIn, quality){
-    this.name = name;
-    this.sellIn = sellIn;
-    this.quality = quality;
+  constructor(name, sellIn, quality) {
+    this.name = name
+    this.sellIn = sellIn
+    this.quality = quality
   }
 }
 
-class Shop {
-  constructor(items=[]){
-    this.items = items;
-  }
-  updateQuality() {
-    for (let i = 0; i < this.items.length; i++) {
-      if (this.items[i].name != 'Aged Brie' && this.items[i].name != 'Backstage passes to a TAFKAL80ETC concert') {
-        if (this.items[i].quality > 0) {
-          if (this.items[i].name != 'Sulfuras, Hand of Ragnaros') {
-            this.items[i].quality = this.items[i].quality - 1;
-          }
-        }
-      } else {
-        if (this.items[i].quality < 50) {
-          this.items[i].quality = this.items[i].quality + 1;
-          if (this.items[i].name == 'Backstage passes to a TAFKAL80ETC concert') {
-            if (this.items[i].sellIn < 11) {
-              if (this.items[i].quality < 50) {
-                this.items[i].quality = this.items[i].quality + 1;
-              }
-            }
-            if (this.items[i].sellIn < 6) {
-              if (this.items[i].quality < 50) {
-                this.items[i].quality = this.items[i].quality + 1;
-              }
-            }
-          }
-        }
-      }
-      if (this.items[i].name != 'Sulfuras, Hand of Ragnaros') {
-        this.items[i].sellIn = this.items[i].sellIn - 1;
-      }
-      if (this.items[i].sellIn < 0) {
-        if (this.items[i].name != 'Aged Brie') {
-          if (this.items[i].name != 'Backstage passes to a TAFKAL80ETC concert') {
-            if (this.items[i].quality > 0) {
-              if (this.items[i].name != 'Sulfuras, Hand of Ragnaros') {
-                this.items[i].quality = this.items[i].quality - 1;
-              }
-            }
-          } else {
-            this.items[i].quality = this.items[i].quality - this.items[i].quality;
-          }
-        } else {
-          if (this.items[i].quality < 50) {
-            this.items[i].quality = this.items[i].quality + 1;
-          }
-        }
-      }
-    }
+const calculateQualityDiffForNormalItem = ({ sellIn, quality }) => {
+  const isQualityGreaterThanZero = quality > 0
+  const cannotSell = sellIn < 0
 
-    return this.items;
+  if (isQualityGreaterThanZero && cannotSell) return -2
+  if (isQualityGreaterThanZero) return -1
+  return 0
+}
+
+const calculateQualityDiffForBackstage = ({ sellIn, quality }) => {
+  const tenDaysOrLessToSell = sellIn <= 10
+  const fiveDaysOrLessToSell = sellIn <= 5
+  const cannotSell = sellIn < 0
+
+  if (cannotSell) return -quality
+  if (fiveDaysOrLessToSell) return +3
+  if (tenDaysOrLessToSell) return +2
+
+  return +1
+}
+
+const calculateSellinDifference = ({ name }) => {
+  const isSulfuras = name == 'Sulfuras'
+  return !isSulfuras ? -1 : 0
+}
+
+const calculateQualityDifference = (item) => {
+  const isSulfuras = item.name == 'Sulfuras'
+  const isAgedBrie = item.name == 'Aged Brie'
+  const isConjuredItem = item.name.includes('Conjured')
+  const isBackstagePasses = item.name == 'Backstage passes'
+  const isQualityLessThan50 = item.quality < 50
+  const isNormalItem =
+    !isAgedBrie && !isBackstagePasses && !isSulfuras && !isConjuredItem
+
+  if (isConjuredItem) return calculateQualityDiffForNormalItem(item) * 2
+  if (isNormalItem) return calculateQualityDiffForNormalItem(item)
+  if (isBackstagePasses) return calculateQualityDiffForBackstage(item)
+  if (isAgedBrie && isQualityLessThan50) return +1
+  return 0
+}
+
+class Shop {
+  constructor(items = []) {
+    this.items = items
+  }
+
+  updateQuality() {
+    return this.items.map((item) => {
+      item.sellIn += calculateSellinDifference(item)
+      item.quality += calculateQualityDifference(item)
+      return item
+    })
   }
 }
 
 module.exports = {
   Item,
-  Shop
+  Shop,
 }
diff --git a/js-jest/test/gilded_rose.test.js b/js-jest/test/gilded_rose.test.js
index c8e0e3d7..512b7089 100644
--- a/js-jest/test/gilded_rose.test.js
+++ b/js-jest/test/gilded_rose.test.js
@@ -1,9 +1,115 @@
-const {Shop, Item} = require("../src/gilded_rose");
+const { Shop, Item } = require('../src/gilded_rose')
 
-describe("Gilded Rose", function() {
-  it("should foo", function() {
-    const gildedRose = new Shop([new Item("foo", 0, 0)]);
-    const items = gildedRose.updateQuality();
-    expect(items[0].name).toBe("fixme");
-  });
-});
+describe('Gilded Rose', function () {
+  it('should foo', function () {
+    const gildedRose = new Shop([new Item('foo', 0, 0)])
+    const items = gildedRose.updateQuality()
+    expect(items[0].name).toBe('foo')
+  })
+
+  it('should return correct result', () => {
+    const storeItems = [
+      new Item('Test Potion', 10, 20),
+      new Item('Aged Brie', 2, 0),
+      new Item('Healing Salve', 5, 7),
+      new Item('Sulfuras', 0, 80),
+      new Item('Backstage passes', 15, 20),
+    ]
+
+    const expectedResult = [
+      new Item('Test Potion', 9, 19),
+      new Item('Aged Brie', 1, 1),
+      new Item('Healing Salve', 4, 6),
+      new Item('Sulfuras', 0, 80),
+      new Item('Backstage passes', 14, 21),
+    ]
+    const gildedRose = new Shop(storeItems)
+    const items = gildedRose.updateQuality()
+
+    expect(items).toStrictEqual(expectedResult)
+  })
+
+  it('Should normal items quality never be below 0', () => {
+    const storeItems = [new Item('Oblivion staff', 10, 0)]
+    const expectedResult = [new Item('Oblivion staff', 9, 0)]
+    const gildedRose = new Shop(storeItems)
+    const items = gildedRose.updateQuality()
+
+    expect(items).toStrictEqual(expectedResult)
+  })
+
+  it('Should quality degrade twice as fast when the sellIn date passes', () => {
+    const storeItems = [new Item('Oblivion staff', 0, 4)]
+    const expectedResult = [new Item('Oblivion staff', -1, 2)]
+    const gildedRose = new Shop(storeItems)
+    const items = gildedRose.updateQuality()
+
+    expect(items).toStrictEqual(expectedResult)
+  })
+
+  it('Should the quality of an item can never be more than 50', () => {
+    const storeItems = [new Item('Aged Brie', 1, 50)]
+    const expectedResult = [new Item('Aged Brie', 0, 50)]
+    const gildedRose = new Shop(storeItems)
+    const items = gildedRose.updateQuality()
+
+    expect(items).toStrictEqual(expectedResult)
+  })
+
+  it('Should quality of an aged brie should increase by 1', () => {
+    const storeItems = [new Item('Aged Brie', 1, 0)]
+    const expectedResult = [new Item('Aged Brie', 0, 1)]
+    const gildedRose = new Shop(storeItems)
+    const items = gildedRose.updateQuality()
+
+    expect(items).toStrictEqual(expectedResult)
+  })
+})
+
+describe('Backstage passes', () => {
+  it("increases in Quality as it's SellIn value approaches", () => {
+    const storeItems = [new Item('Backstage passes', 14, 0)]
+    const expectedResult = [new Item('Backstage passes', 13, 1)]
+    const gildedRose = new Shop(storeItems)
+    const items = gildedRose.updateQuality()
+
+    expect(items).toStrictEqual(expectedResult)
+  })
+
+  it('Quality increases by 2 when there are 10 days or less', () => {
+    const storeItems = [new Item('Backstage passes', 10, 0)]
+    const expectedResult = [new Item('Backstage passes', 9, 2)]
+    const gildedRose = new Shop(storeItems)
+    const items = gildedRose.updateQuality()
+
+    expect(items).toStrictEqual(expectedResult)
+  })
+
+  it('Quality increases by 3 when there are 5 days or less', () => {
+    const storeItems = [new Item('Backstage passes', 5, 0)]
+    const expectedResult = [new Item('Backstage passes', 4, 3)]
+    const gildedRose = new Shop(storeItems)
+    const items = gildedRose.updateQuality()
+
+    expect(items).toStrictEqual(expectedResult)
+  })
+
+  it('Quality drops to 0 after concert', () => {
+    const storeItems = [new Item('Backstage passes', 0, 30)]
+    const expectedResult = [new Item('Backstage passes', -1, 0)]
+    const gildedRose = new Shop(storeItems)
+    const items = gildedRose.updateQuality()
+
+    expect(items).toStrictEqual(expectedResult)
+  })
+})
+describe('Conjured items', () => {
+  it('Should quality of conjured items decrease twice as fast', () => {
+    const storeItems = [new Item('Conjured Test Cake', 10, 20)]
+    const expectedResult = [new Item('Conjured Test Cake', 9, 18)]
+    const gildedRose = new Shop(storeItems)
+    const items = gildedRose.updateQuality()
+
+    expect(items).toStrictEqual(expectedResult)
+  })
+})