From c048d180e09a0665b600b6b921399a8c43efb401 Mon Sep 17 00:00:00 2001
From: Nik Bezdzenariy <kartoshkinkapustin@gmail.com>
Date: Fri, 10 Apr 2026 17:14:04 +0200
Subject: [PATCH 1/4] fix(debug): resolve scope errors in module data

---
 Sprint-2/debug/address.js |  4 +++-
 Sprint-2/debug/author.js  | 10 +++++++---
 Sprint-2/debug/recipe.js  |  3 ++-
 3 files changed, 12 insertions(+), 5 deletions(-)

diff --git a/Sprint-2/debug/address.js b/Sprint-2/debug/address.js
index 940a6af83..9f28f0468 100644
--- a/Sprint-2/debug/address.js
+++ b/Sprint-2/debug/address.js
@@ -1,4 +1,6 @@
 // Predict and explain first...
+// objects are not arrays and don`t have ordinal numbers (0, 1, 2)
+// their data is accessed by keys (names)
 
 // This code should log out the houseNumber from the address object
 // but it isn't working...
@@ -12,4 +14,4 @@ const address = {
   postcode: "XYZ 123",
 };
 
-console.log(`My house number is ${address[0]}`);
+console.log(`My house number is ${address.houseNumber}`);
diff --git a/Sprint-2/debug/author.js b/Sprint-2/debug/author.js
index 8c2125977..329f215b4 100644
--- a/Sprint-2/debug/author.js
+++ b/Sprint-2/debug/author.js
@@ -1,4 +1,8 @@
 // Predict and explain first...
+// for...of loop
+// designed for arrays
+// doesn't work with objects
+// objects in JS are not iterable
 
 // This program attempts to log out all the property values in the object.
 // But it isn't working. Explain why first and then fix the problem
@@ -11,6 +15,6 @@ const author = {
   alive: true,
 };
 
-for (const value of author) {
-  console.log(value);
-}
+for (const value of Object.values(author)) {
+  console.log (value);
+}
\ No newline at end of file
diff --git a/Sprint-2/debug/recipe.js b/Sprint-2/debug/recipe.js
index 6cbdd22cd..2b4a55aa1 100644
--- a/Sprint-2/debug/recipe.js
+++ b/Sprint-2/debug/recipe.js
@@ -1,4 +1,5 @@
 // Predict and explain first...
+// ${recipe} object inserted in console.log.
 
 // This program should log out the title, how many it serves and the ingredients.
 // Each ingredient should be logged on a new line
@@ -12,4 +13,4 @@ const recipe = {
 
 console.log(`${recipe.title} serves ${recipe.serves}
   ingredients:
-${recipe}`);
+${recipe.ingredients.join(`\n`)}`);

From 87fed8e8af4c1c654fcd2907424feb82cdec9402 Mon Sep 17 00:00:00 2001
From: Nik Bezdzenariy <kartoshkinkapustin@gmail.com>
Date: Fri, 10 Apr 2026 17:14:24 +0200
Subject: [PATCH 2/4] feat(implement): add lookup and tally logic

---
 Sprint-2/implement/contains.js         | 10 ++++-
 Sprint-2/implement/contains.test.js    | 24 +++++++++++-
 Sprint-2/implement/lookup.js           | 42 +++++++++++++++++++-
 Sprint-2/implement/lookup.test.js      | 54 +++++++++++++++++++++++++-
 Sprint-2/implement/querystring.js      | 18 ++++++++-
 Sprint-2/implement/querystring.test.js | 19 +++++++++
 Sprint-2/implement/tally.js            | 13 ++++++-
 Sprint-2/implement/tally.test.js       | 16 +++++++-
 8 files changed, 187 insertions(+), 9 deletions(-)

diff --git a/Sprint-2/implement/contains.js b/Sprint-2/implement/contains.js
index cd779308a..c9451f8a1 100644
--- a/Sprint-2/implement/contains.js
+++ b/Sprint-2/implement/contains.js
@@ -1,3 +1,11 @@
-function contains() {}
+function contains(obj, key) {
+    // check if obj is actually an obj not null or array
+    if (!obj || typeof obj !== 'object' || Array.isArray(obj)) {
+        return false;
+    }
+
+    // use 'in' operator to check if key exists in object
+    return key in obj;
+}
 
 module.exports = contains;
diff --git a/Sprint-2/implement/contains.test.js b/Sprint-2/implement/contains.test.js
index 326bdb1f2..750a7c8c2 100644
--- a/Sprint-2/implement/contains.test.js
+++ b/Sprint-2/implement/contains.test.js
@@ -1,5 +1,28 @@
 const contains = require("./contains.js");
 
+test ("returns false for empty object", () => {
+    expect(contains({}, 'a')).toBe(false);
+});
+
+test("returns true when property exists", () => {
+    expect(contains({a: 1,  b: 2}, 'a')).toBe(true);
+    expect(contains({name: 'John'}, 'name')).toBe(true);
+});
+
+test("returns false when property doesn't exist", () => {
+    expect(contains({a: 1, b: 2}, 'c')).toBe(false);
+    expect(contains({x: 10}, 'y')).toBe(false);
+});
+
+test("returns false for invalid input (array)", () => {
+    expect(contains([1, 2, 3], '0')).toBe(false);
+});
+
+test("returns false for null or undefined", () => {
+    expect(contains(null, 'a')).toBe(false);
+    expect(contains(undefined, 'a')).toBe(false);
+});
+
 /*
 Implement a function called contains that checks an object contains a
 particular property
@@ -20,7 +43,6 @@ as the object doesn't contains a key of 'c'
 // Given an empty object
 // When passed to contains
 // Then it should return false
-test.todo("contains on empty object returns false");
 
 // Given an object with properties
 // When passed to contains with an existing property name
diff --git a/Sprint-2/implement/lookup.js b/Sprint-2/implement/lookup.js
index a6746e07f..e579e8ab4 100644
--- a/Sprint-2/implement/lookup.js
+++ b/Sprint-2/implement/lookup.js
@@ -1,5 +1,45 @@
-function createLookup() {
+/**
+ * creates a lookup object from an array of key-value pairs
+ * 
+ * @param {Array<Array<string>>} pairs - array of [key, value] pairs
+ * @returns {Object} - lookup object with keys mapped to values
+ * @throws {Typeerror} - if input is not a valid array of pairs
+ * 
+ * @example 
+ * createLookup([['US', 'USD'], ['CA', 'CAD']])
+ * // Returns: { US: 'USD', CA: 'CAD' }
+ */
+function createLookup(pairs) {
   // implementation here
+  // 1. validate input
+  if (!Array.isArray(pairs)) {
+    throw new TypeError('Input must be an array');
+  }
+
+  // 2. initialize empty result object
+  const lookup = {};
+
+  // 3. iterate through each pair
+  for (const pair of pairs) {
+    // 3a. validate each pair: must be an array with 2 elements
+    if (!Array.isArray(pair) || pair.length !== 2) {
+      throw new TypeError('Each pair must be an array of exactly 2 elements');
+    }
+
+    // 3b. extract key and value
+    const [key, value] = pair; // destructing assignment
+
+    // 3c. validate key must be a string
+    if (typeof key !== 'string') {
+      throw new TypeError('Keys must be stings');
+    }
+
+    // 3d. add to lookup object
+    lookup[key] = value;
+  }
+
+  // 4. return the constructed lookup object
+  return lookup;
 }
 
 module.exports = createLookup;
diff --git a/Sprint-2/implement/lookup.test.js b/Sprint-2/implement/lookup.test.js
index 547e06c5a..21b18dd71 100644
--- a/Sprint-2/implement/lookup.test.js
+++ b/Sprint-2/implement/lookup.test.js
@@ -1,9 +1,59 @@
 const createLookup = require("./lookup.js");
 
-test.todo("creates a country currency code lookup for multiple codes");
+// happy path: valid input
+test("creates a lookup object from valid pairs", () => {
+  const pairs = [['US', 'USD'], ['CA', 'CAD']];
+  const result = createLookup(pairs);
 
-/*
+  expect(result).toEqual({
+    US: 'USD',
+    CA: 'CAD'
+  });
+});
 
+// empty array
+test("returns empty object for empty array", () => {
+  expect(createLookup([])).toEqual({});
+});
+
+// single pair
+test("handle single pair correctly", () => {
+  const pairs = [['UK', 'GBP']];
+  expect(createLookup(pairs)).toEqual({ UK: 'GBP' });
+});
+
+// duplicates keys (last value wins)
+test("handle duplicates keys by keeping last value", () => {
+  const pairs = [['US', 'USD'], ['US', 'EUR']];
+  expect(createLookup(pairs)).toEqual({ US: 'EUR' });
+});
+
+// error handling: not an array
+test("throws TypeError when input is not an array", () => {
+  expect(() => createLookup(null)).toThrow(TypeError);
+  expect(() => createLookup('invalid')).toThrow(TypeError);
+  expect(() => createLookup({a: 1})).toThrow(TypeError);
+});
+
+// error handling: invalid pair (not array)
+test("throws TypeError when pair is not an array", () => {
+  const pairs = [['US', 'USD'], 'invalid'];
+  expect(() => createLookup(pairs)).toThrow(TypeError);
+});
+
+// error handling: invalid pair (wrong length)
+test("throws TypeError when pair has wrong length", () => {
+  const pairs = [['US', 'USD'], ['CA']]; // missing value
+  expect(() => createLookup(pairs)).toThrow(TypeError);
+});
+
+// error handling: non-string key
+test("throws TypeError when key is not a string", () => {
+  const pairs = [[42, 'USD']]; // number as key
+  expect(() => createLookup(pairs)).toThrow(TypeError);
+});
+
+/**
 Create a lookup object of key value pairs from an array of code pairs
 
 Acceptance Criteria:
diff --git a/Sprint-2/implement/querystring.js b/Sprint-2/implement/querystring.js
index 45ec4e5f3..ab9ad74c8 100644
--- a/Sprint-2/implement/querystring.js
+++ b/Sprint-2/implement/querystring.js
@@ -1,12 +1,26 @@
 function parseQueryString(queryString) {
   const queryParams = {};
-  if (queryString.length === 0) {
+  if (!queryString || queryString.length === 0) {
     return queryParams;
   }
+
   const keyValuePairs = queryString.split("&");
 
   for (const pair of keyValuePairs) {
-    const [key, value] = pair.split("=");
+    // divide only by the first sign '='
+    const firstEqualIndex = pair.indexOf("=");
+
+    // If there is no '=',
+    // consider it a key without a value (or skip it)
+    if (firstEqualIndex === -1) {
+      queryParams[pair] = "";
+      continue;
+    }
+
+    const key = pair.slice(0, firstEqualIndex);
+    const value = pair.slice(firstEqualIndex +1);
+
+    // const [key, value] = pair.split("=");
     queryParams[key] = value;
   }
 
diff --git a/Sprint-2/implement/querystring.test.js b/Sprint-2/implement/querystring.test.js
index 3e218b789..e716caeac 100644
--- a/Sprint-2/implement/querystring.test.js
+++ b/Sprint-2/implement/querystring.test.js
@@ -10,3 +10,22 @@ test("parses querystring values containing =", () => {
     "equation": "x=y+1",
   });
 });
+
+test("handles keys without values", () => {
+  expect(parseQueryString("name")).toEqual({ name: ""});
+});
+
+test("handles empty values", () => {
+  expect(parseQueryString("name=")).toEqual({ name: "" });
+});
+
+test("parses simple query string", () => {
+  expect(parseQueryString("name=John&age=30")).toEqual({
+    name: "John",
+    age: "30",
+  });
+});
+
+test("returns empty objects for empty strings", () => {
+  expect(parseQueryString("")).toEqual({});
+});
diff --git a/Sprint-2/implement/tally.js b/Sprint-2/implement/tally.js
index f47321812..750096cb5 100644
--- a/Sprint-2/implement/tally.js
+++ b/Sprint-2/implement/tally.js
@@ -1,3 +1,14 @@
-function tally() {}
+function tally(items) {
+    if(!Array.isArray(items)) {
+        throw new TypeError("Input must be an array");
+    }
+
+    const counts = {};
+    for (const item of items) {
+        // for no key, initialize 0 and add 1
+        counts[item] = (counts[item] || 0) + 1;
+    }
+    return counts;
+}
 
 module.exports = tally;
diff --git a/Sprint-2/implement/tally.test.js b/Sprint-2/implement/tally.test.js
index 2ceffa8dd..9481e40c0 100644
--- a/Sprint-2/implement/tally.test.js
+++ b/Sprint-2/implement/tally.test.js
@@ -1,5 +1,20 @@
 const tally = require("./tally.js");
 
+test("tally on an empty array returns an empty object", () => {
+    expect(tally([])).toEqual({});
+});
+
+test("tally counts frequency of items in an array", () => {
+    expect(tally(['a'])).toEqual({ a: 1 });
+    expect(tally(['a', 'a', 'a'])).toEqual({ a: 3 });
+    expect(tally(['a', 'a', 'b', 'c'])).toEqual({ a:2, b:1, c:1});;
+});
+
+test("tally throws TypeError on invalid input", () => {
+    expect(() => tally("not an array")).toThrow(TypeError);
+    expect(() => tally(null)).toThrow(TypeError);
+});
+
 /**
  * tally array
  *
@@ -23,7 +38,6 @@ const tally = require("./tally.js");
 // Given an empty array
 // When passed to tally
 // Then it should return an empty object
-test.todo("tally on an empty array returns an empty object");
 
 // Given an array with duplicate items
 // When passed to tally

From 20d1179fbcbb89f8ed868ce8b5a10b078cfbb337 Mon Sep 17 00:00:00 2001
From: Nik Bezdzenariy <kartoshkinkapustin@gmail.com>
Date: Sat, 11 Apr 2026 20:10:15 +0200
Subject: [PATCH 3/4] fix(sprint-2): correct typo in invert.js type validation

---
 Sprint-2/interpret/invert.js      | 33 ++++++++++++++++++++++++++++++-
 Sprint-2/interpret/invert.test.js | 29 +++++++++++++++++++++++++++
 2 files changed, 61 insertions(+), 1 deletion(-)
 create mode 100644 Sprint-2/interpret/invert.test.js

diff --git a/Sprint-2/interpret/invert.js b/Sprint-2/interpret/invert.js
index bb353fb1f..8269000d2 100644
--- a/Sprint-2/interpret/invert.js
+++ b/Sprint-2/interpret/invert.js
@@ -7,23 +7,54 @@
 // E.g. invert({x : 10, y : 20}), target output: {"10": "x", "20": "y"}
 
 function invert(obj) {
+  // 1. valiadate input 
+  if (!obj || typeof obj !== 'object' || Array.isArray(obj)) {
+    throw new TypeError('Input must be a plain object');
+  }
+
+  // 2. initialize empty results object
   const invertedObj = {};
 
+  // 3. iterate through key-value pairs
   for (const [key, value] of Object.entries(obj)) {
-    invertedObj.key = value;
+    // 4. swap: value becomes key, bey becomes value
+    invertedObj[value] = key;
   }
 
   return invertedObj;
 }
 
+module.exports = invert;
+
 // a) What is the current return value when invert is called with { a : 1 }
+// invert({ a: 1 })
+// Result: { key: 1 }
+// invertedObj.key = value → creates a "key" property (string), not a key variable
 
 // b) What is the current return value when invert is called with { a: 1, b: 2 }
+// invert({ a: 1, b: 2 })
+// Result: { key: 2 }
+// First iteration: { key: 1 }
+// Second iteration: { key: 2 } ← overwritten!
 
 // c) What is the target return value when invert is called with {a : 1, b: 2}
+// result:
+// { "1": "a", "2": "b" }
+// Values ​​become keys, keys become values
 
 // c) What does Object.entries return? Why is it needed in this program?
+// Object.entries({ a: 1, b: 2 })
+// returns: [["a", 1], ["b", 2]]
+// Why is this necessary?
+// To access both the key and the value simultaneously
+// Destructuring is used: const [key, value] = ["a", 1]
 
 // d) Explain why the current return value is different from the target output
+// 1. Dot notation instead of bracket notation:
+// invertedObj.key = value; // ❌ Creates a "key" property (string)
+// invertedObj[key] = value; // ✅ Uses the value of the key variable
+// 2. Incorrect key-value order:
+// invertedObj[key] = value; // ❌ Key remains the key
+// invertedObj[value] = key; // ✅ Value becomes the key
 
 // e) Fix the implementation of invert (and write tests to prove it's fixed!)
diff --git a/Sprint-2/interpret/invert.test.js b/Sprint-2/interpret/invert.test.js
new file mode 100644
index 000000000..4424fa6b7
--- /dev/null
+++ b/Sprint-2/interpret/invert.test.js
@@ -0,0 +1,29 @@
+const invert = require("./invert.js");
+
+// happy path
+test("inverts a single key-value pair", () => {
+    expect(invert({ a: 1})).toEqual({ "1": "a" });
+});
+
+test("inverts with string values", () => {
+    expect(invert({ x: "hello", y: "world" })).toEqual({
+        hello: "x",
+        world: "y"
+    });
+});
+
+// edge cases
+test("handles empty pbject", () => {
+    expect(invert({})).toEqual({});
+});
+
+test("handles duplicate values (last key wins)", () => {
+    expect(invert({ a:1, b: 1 })).toEqual({ "1": "b" });
+});
+
+// error handling
+test("throws TypeError for invalid input", () => {
+    expect(() => invert(null)).toThrow(TypeError);
+    expect(() => invert([1, 2])).toThrow(TypeError);
+    expect(() => invert("string")).toThrow(TypeError);
+});
\ No newline at end of file

From 095a8ae52e1e8bfd73d25b024427394f5f1b2131 Mon Sep 17 00:00:00 2001
From: Nik Bezdzenariy <kartoshkinkapustin@gmail.com>
Date: Sun, 12 Apr 2026 13:48:14 +0200
Subject: [PATCH 4/4] feat(sprint-2): complete stretch tasks and tests

---
 Sprint-2/stretch/count-words.js      | 54 +++++++++++++++++++++++++
 Sprint-2/stretch/count-words.test.js | 59 ++++++++++++++++++++++++++++
 Sprint-2/stretch/mode.js             | 47 ++++++++++++++++++++++
 Sprint-2/stretch/till.js             | 35 +++++++++++++++++
 Sprint-2/stretch/totalTill.test.js   | 54 +++++++++++++++++++++++++
 5 files changed, 249 insertions(+)
 create mode 100644 Sprint-2/stretch/count-words.test.js
 create mode 100644 Sprint-2/stretch/totalTill.test.js

diff --git a/Sprint-2/stretch/count-words.js b/Sprint-2/stretch/count-words.js
index 8e85d19d7..eaf430415 100644
--- a/Sprint-2/stretch/count-words.js
+++ b/Sprint-2/stretch/count-words.js
@@ -26,3 +26,57 @@
 
 3. Order the results to find out which word is the most common in the input
 */
+
+/**
+ * counts the frequency of words in aa string.
+ * 
+ * @param {string} text - the input string
+ * @returns {object} - object with words as keys and counts as values
+ * 
+ * @example
+ * countWords("hello world hello")
+ * // returns: { hello: 2, world: 1 }
+ */
+function countWords(text) {
+  // 1. validate input type
+  if (typeof text !== 'string') {
+    throw new TypeError('Input must be a string');
+  }
+
+  // 2. handle empty string edge case
+  if (text.length === 0) {
+    return {};
+  }
+
+  // 3. convert to lowercase (ignore case)
+  const lowerText = text.toLowerCase();
+
+  // 4. remove punctuation (adv challenge)
+  // replace all non-word char (except spaces) with empty str
+  // /[^\w\s]/g - replaces everything that is NOT (^) a word char (\w) or whitespace (\s)
+  const cleanText = lowerText.replace(/[^\w\s]/g, '');
+
+  // 5. split into words
+  // /\s+/ - splits by one or more (+) whitespace characters (\s)
+  const words = cleanText.split(/\s+/); // split by one or more spaces
+
+  // 6. initialize empty result objects
+  const counts = {};
+
+  // 7. count each word
+  for (const word of words) {
+    // skip empty strings (from extra spaces at start/end)
+    if (word === '') {
+      continue;
+    }
+    
+    // increment counter using tally pattern
+    // Tally pattern: if key doesn't exist (undefined), use 0, then add 1
+    counts[word] = (counts[word] || 0) + 1;
+  }
+
+  // 8. return counts object
+  return counts;
+}
+
+module.exports = countWords
\ No newline at end of file
diff --git a/Sprint-2/stretch/count-words.test.js b/Sprint-2/stretch/count-words.test.js
new file mode 100644
index 000000000..285e944e4
--- /dev/null
+++ b/Sprint-2/stretch/count-words.test.js
@@ -0,0 +1,59 @@
+const countWords = require("./count-words.js")
+
+// basic func
+test("counts word frequency", () => {
+    expect(countWords("you and me and you")).toEqual({
+        you: 2,
+        and: 2,
+        me: 1
+    });
+});
+
+// edge cases: empty sting
+test("returns empty object for empty string", () => {
+    expect(countWords("     ")).toEqual({});
+});
+
+// case insensitivity
+test("ignores case", () => {
+    expect(countWords("Hello hello HELLO")).toEqual({
+        hello: 3
+    });
+});
+
+// punctuation removal
+test("removes punctuation", () => {
+    expect(countWords("hello, world!")).toEqual({
+        hello: 1,
+        world: 1
+    });
+});
+
+// multiple spaces
+test("handles multiple spaces", () => {
+    expect(countWords("word1    word2")).toEqual({
+        word1: 1,
+        word2: 1
+    });
+});
+
+// error handling
+test("throws TypeError for non-string input", () => {
+    expect(() => countWords(123)).toThrow(TypeError);
+    expect(() => countWords(null)).toThrow(TypeError);
+    expect(() => countWords(undefined)).toThrow(TypeError);
+});
+
+// complex example
+test("handles complex sentence", () => {
+    expect(countWords("The quick brown fox jumps over the lazy dog")).toEqual({
+        the: 2,
+        quick: 1,
+        brown: 1,
+        fox: 1,
+        jumps: 1,
+        over: 1,
+        lazy: 1,
+        dog: 1
+    });
+});
\ No newline at end of file
diff --git a/Sprint-2/stretch/mode.js b/Sprint-2/stretch/mode.js
index 3f7609d79..05fa30112 100644
--- a/Sprint-2/stretch/mode.js
+++ b/Sprint-2/stretch/mode.js
@@ -8,6 +8,11 @@
 // refactor calculateMode by splitting up the code
 // into smaller functions using the stages above
 
+/*
+// given an implementation of calculateMode
+// refactor by splitting into smaller functions
+
+// 1. track frequency of each value
 function calculateMode(list) {
   // track frequency of each value
   let freqs = new Map();
@@ -34,3 +39,45 @@ function calculateMode(list) {
 }
 
 module.exports = calculateMode;
+*/
+
+function getFrequencies(list) {
+  const freqs = new Map();
+
+  for (const num of list) {
+    if (typeof num !== 'number') {
+      continue;
+    }
+
+    freqs.set(num, (freqs.get(num) || 0) + 1);
+  }
+
+  return freqs;
+}
+
+// stage 2: find the value with the highest frequency
+function findMode(freqs) {
+  let maxFreq = 0;
+  let mode = NaN;
+
+  for (const [num, freq] of freqs) {
+    if(freq > maxFreq) {
+      mode = num;
+      maxFreq = freq;
+    }
+  }
+  
+  return mode;
+}
+
+// main function (refactored)
+function calculateMode(list) {
+  if (!Array.isArray(list) || list.length === 0) {
+    return NaN;
+  }
+
+  const frequencies = getFrequencies(list);
+  return findMode(frequencies);
+}
+
+module.exports = calculateMode;
\ No newline at end of file
diff --git a/Sprint-2/stretch/till.js b/Sprint-2/stretch/till.js
index 6a08532e7..9af0b3e32 100644
--- a/Sprint-2/stretch/till.js
+++ b/Sprint-2/stretch/till.js
@@ -4,6 +4,7 @@
 // When this till object is passed to totalTill
 // Then it should return the total amount in pounds
 
+/*
 function totalTill(till) {
   let total = 0;
 
@@ -23,9 +24,43 @@ const till = {
 const totalAmount = totalTill(till);
 
 // a) What is the target output when totalTill is called with the till object
+// bug:
+// "1p" * 10 // NaN (string × number = NaN)
 
 // b) Why do we need to use Object.entries inside the for...of loop in this function?
+// to get both key and value simultaneously through destructuring.
+// Object.entries() turns an object into an array of [key, value] pairs:
+Object.entries(till)
+[["1p", 10], ["5p", 6], ["50p", 4], ["20p", 10]]
+// allows to use destructuring in a loop:
+for (const [coin, quantity] of Object.entries(till)) {
+// coin = "1p", quantity = 10
+}
 
 // c) What does coin * quantity evaluate to inside the for...of loop?
+// NaN because "1p" is a string, not a number.
+// therefore, doesn't work
 
 // d) Write a test for this function to check it works and then fix the implementation of totalTill
+// fix: use parseInt(coin) to extract a number from a string.
+*/
+
+// totalTill takes an object representing coins in a till
+
+function totalTill(till) {
+  let totalInPence = 0;
+
+  for (const [coin, quantity] of Object.entries(till)) {
+    // extract number from string "50p" -> 50
+    const coinValue = parseInt(coin);
+
+    if (!isNaN(coinValue)) {
+      totalInPence += coinValue * quantity;
+    }
+  }
+
+  // convert pence to pounds and format to 2 decimal places
+  return `£${(totalInPence / 100).toFixed(2)}`;
+}
+
+module.exports = totalTill;
\ No newline at end of file
diff --git a/Sprint-2/stretch/totalTill.test.js b/Sprint-2/stretch/totalTill.test.js
new file mode 100644
index 000000000..ea3bbcbbe
--- /dev/null
+++ b/Sprint-2/stretch/totalTill.test.js
@@ -0,0 +1,54 @@
+const totalTill = require("./till.js");
+
+// basic func
+test("calculates total amount in pounds", () => {
+    const till = {
+        "1p": 10,
+        "5p": 6,
+        "50p": 4,
+        "20p": 10,
+    };
+
+    expect (totalTill(till)).toBe("£4.40");
+});
+
+// edge case: empty till
+test("handles empty till", () => {
+    expect(totalTill({})).toBe("£0.00");
+});
+
+// single coin type
+test("handles single coin type", () => {
+    const till = {
+        "1p": 100,
+    };
+
+    expect(totalTill(till)).toBe("£1.00");
+});
+
+// large amounts
+test("handle large amounts", () => {
+    const till = {
+        "1p": 50,
+        "2p": 50,
+        "5p": 20,
+        "10p": 10,
+        "20p": 5,
+        "50p": 2,
+        "100p": 1, // £1 coin
+        "200p": 1, // £2 coin
+     };
+
+    // 50 + 100 + 100 + 100 + 100 + 100 + 100 + 200 = 850p = £8.50
+     expect(totalTill(till)).toBe("£8.50");  
+});
+
+// zero quantities
+test("handles zero quantites", () => {
+    const till = {
+        "1p": 0,
+        "5p": 0,
+    };
+
+    expect(totalTill(till)).toBe("£0.00");
+});
\ No newline at end of file