From 7ef97ad0aac64cfce9ac6a2aa02b87f44e7c3cd6 Mon Sep 17 00:00:00 2001
From: Khor Biel <khorkoak@gmail.com>
Date: Wed, 12 Nov 2025 01:19:51 +0000
Subject: [PATCH 1/4] Completed Sprint 2 Implement tasks (contains, lookup,
 tally, querystring) with passing tests

---
 Sprint-2/debug/address.js           |  2 +-
 Sprint-2/debug/author.js            | 15 +++++++++--
 Sprint-2/debug/recipe.js            | 12 ++++++++-
 Sprint-2/implement/contains.js      | 10 ++++++-
 Sprint-2/implement/contains.test.js | 14 +++++++++-
 Sprint-2/implement/lookup.js        | 12 +++++++--
 Sprint-2/implement/lookup.test.js   | 17 +++++++++++-
 Sprint-2/implement/querystring.js   | 22 ++++++++++++---
 Sprint-2/implement/tally.js         | 21 ++++++++++++++-
 Sprint-2/implement/tally.test.js    | 10 ++++++-
 Sprint-2/interpret/invert.js        | 42 +++++++++++++++++++++++------
 11 files changed, 155 insertions(+), 22 deletions(-)

diff --git a/Sprint-2/debug/address.js b/Sprint-2/debug/address.js
index 940a6af83..36d2f865d 100644
--- a/Sprint-2/debug/address.js
+++ b/Sprint-2/debug/address.js
@@ -12,4 +12,4 @@ 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..f0b1a2dbb 100644
--- a/Sprint-2/debug/author.js
+++ b/Sprint-2/debug/author.js
@@ -11,6 +11,17 @@ const author = {
   alive: true,
 };
 
-for (const value of author) {
+// Prediction:
+// The code will not log the property values of the author object as intended.
+// This causes the error because author is not iterable.
+
+ // Explanation:
+
+// The original code likely used a for...in loop which iterates over the keys of the object, not the values.
+// Therefore, logging the key would not give the desired property values.
+// By using Object.values(author), we can directly iterate over the values of the object.
+
+// Fixed code:
+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..d9d7678ae 100644
--- a/Sprint-2/debug/recipe.js
+++ b/Sprint-2/debug/recipe.js
@@ -10,6 +10,16 @@ const recipe = {
   ingredients: ["olive oil", "tomatoes", "salt", "pepper"],
 };
 
+
+// Prediction:
+// The code will not log the ingredients correctly because it is trying to log the entire recipe object instead of just the ingredients array.
+// This will result in an output that includes the object structure rather than the individual ingredients.
+
+// Explanation:
+// The template literal is incorrectly using `${recipe}` which outputs the whole object instead of iterating over the ingredients array.
+// To fix this, we need to access the ingredients property and format it correctly, possibly by joining the array elements with new line characters.
+
+// Fixed code:
 console.log(`${recipe.title} serves ${recipe.serves}
   ingredients:
-${recipe}`);
+${recipe.ingredients.join('\n')}`);
\ No newline at end of file
diff --git a/Sprint-2/implement/contains.js b/Sprint-2/implement/contains.js
index cd779308a..0f9373e2f 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 the first argument is a valid object
+  if (typeof obj !== "object" || obj === null || Array.isArray(obj)) {
+    return false;
+  }
+
+  // Check if the key exists in the object
+  return Object.prototype.hasOwnProperty.call(obj, key);
+}
 
 module.exports = contains;
diff --git a/Sprint-2/implement/contains.test.js b/Sprint-2/implement/contains.test.js
index 326bdb1f2..d32c99356 100644
--- a/Sprint-2/implement/contains.test.js
+++ b/Sprint-2/implement/contains.test.js
@@ -20,16 +20,28 @@ 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");
+test("contains on empty object returns false", () => {
+  expect(contains({}, "a")).toBe(false);
+});
+
 
 // Given an object with properties
 // When passed to contains with an existing property name
 // Then it should return true
+test("contains on object with existing property returns true", () => {
+  expect(contains({ a: 1, b: 2 }, "a")).toBe(true);
+});
 
 // Given an object with properties
 // When passed to contains with a non-existent property name
 // Then it should return false
+test("contains on object with non-existent property returns false", () => {
+  expect(contains({ a: 1, b: 2 }, "c")).toBe(false);
+});
 
 // Given invalid parameters like an array
 // When passed to contains
 // Then it should return false or throw an error
+test("contains on invalid parameters returns false", () => {
+  expect(contains([], "a")).toBe(false);
+});
diff --git a/Sprint-2/implement/lookup.js b/Sprint-2/implement/lookup.js
index a6746e07f..b30c2f990 100644
--- a/Sprint-2/implement/lookup.js
+++ b/Sprint-2/implement/lookup.js
@@ -1,5 +1,13 @@
-function createLookup() {
-  // implementation here
+function createLookup(countryCurrencyPairs) {
+   const lookup = {};
+
+   for (const pair of countryCurrencyPairs) {
+     const countryCode = pair[0];
+     const currencyCode = pair[1];
+     lookup[countryCode] = currencyCode;
+   }
+
+   return lookup;
 }
 
 module.exports = createLookup;
diff --git a/Sprint-2/implement/lookup.test.js b/Sprint-2/implement/lookup.test.js
index 547e06c5a..75d077a31 100644
--- a/Sprint-2/implement/lookup.test.js
+++ b/Sprint-2/implement/lookup.test.js
@@ -1,6 +1,21 @@
 const createLookup = require("./lookup.js");
 
-test.todo("creates a country currency code lookup for multiple codes");
+test("creates a country currency code lookup for multiple codes", () => {
+  // Given: An array of arrays representing country code and currency code pairs
+  const countryCurrencyPairs = [
+    ["US", "USD"],
+    ["CA", "CAD"],
+  ];
+
+  // When: createLookup function is called with the country-currency array
+  const result = createLookup(countryCurrencyPairs);
+
+  // Then: It should return an object where keys are country codes and values are currency codes
+  expect(result).toEqual({
+    US: "USD",
+    CA: "CAD",
+  });
+});
 
 /*
 
diff --git a/Sprint-2/implement/querystring.js b/Sprint-2/implement/querystring.js
index 45ec4e5f3..de7074099 100644
--- a/Sprint-2/implement/querystring.js
+++ b/Sprint-2/implement/querystring.js
@@ -1,13 +1,29 @@
 function parseQueryString(queryString) {
   const queryParams = {};
-  if (queryString.length === 0) {
+
+  if (!queryString || queryString.length === 0) {
     return queryParams;
   }
+
+  // Remove leading '?' if present
+  if (queryString.startsWith("?")) {
+    queryString = queryString.substring(1);
+  }
+
   const keyValuePairs = queryString.split("&");
 
   for (const pair of keyValuePairs) {
-    const [key, value] = pair.split("=");
-    queryParams[key] = value;
+    // Only split on the first '=' to handle values containing '='
+    const equalsIndex = pair.indexOf("=");
+    if (equalsIndex === -1) {
+      // Handle keys without values
+      const key = decodeURIComponent(pair);
+      queryParams[key] = "";
+    } else {
+      const key = decodeURIComponent(pair.substring(0, equalsIndex));
+      const value = decodeURIComponent(pair.substring(equalsIndex + 1));
+      queryParams[key] = value;
+    }
   }
 
   return queryParams;
diff --git a/Sprint-2/implement/tally.js b/Sprint-2/implement/tally.js
index f47321812..885a33825 100644
--- a/Sprint-2/implement/tally.js
+++ b/Sprint-2/implement/tally.js
@@ -1,3 +1,22 @@
-function tally() {}
+function tally(items) {
+  // Validate input
+  if (!Array.isArray(items)) {
+    throw new Error("Input must be an array");
+  }
+
+  // Start with an empty object
+  const result = {};
+
+  // Loop through the array and count
+  for (const item of items) {
+    if (result[item]) {
+      result[item] += 1;
+    } else {
+      result[item] = 1;
+    }
+  }
+
+  return result;
+}
 
 module.exports = tally;
diff --git a/Sprint-2/implement/tally.test.js b/Sprint-2/implement/tally.test.js
index 2ceffa8dd..69a328501 100644
--- a/Sprint-2/implement/tally.test.js
+++ b/Sprint-2/implement/tally.test.js
@@ -23,12 +23,20 @@ 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");
+test("tally on an empty array returns an empty object", () => {
+  expect(tally([])).toEqual({});
+});
 
 // Given an array with duplicate items
 // When passed to tally
 // Then it should return counts for each unique item
+test("returns correct counts for array with duplicate items", () => {
+  expect(tally(["a", "a", "b", "c"])).toEqual({ a: 2, b: 1, c: 1 });
+});
 
 // Given an invalid input like a string
 // When passed to tally
 // Then it should throw an error
+test("throws an error for invalid input (not an array)", () => {
+  expect(() => tally("a")).toThrow("Input must be an array");
+});
diff --git a/Sprint-2/interpret/invert.js b/Sprint-2/interpret/invert.js
index bb353fb1f..76cd7825d 100644
--- a/Sprint-2/interpret/invert.js
+++ b/Sprint-2/interpret/invert.js
@@ -6,24 +6,50 @@
 
 // E.g. invert({x : 10, y : 20}), target output: {"10": "x", "20": "y"}
 
-function invert(obj) {
-  const invertedObj = {};
-
-  for (const [key, value] of Object.entries(obj)) {
-    invertedObj.key = value;
-  }
 
-  return invertedObj;
-}
 
 // a) What is the current return value when invert is called with { a : 1 }
+// Object.entries({ a: 1 }) → [["a", 1]]
+// The loop runs once with key = "a" and value = 1
+// Inside the loop:
+// invertedObj.key = value;
+// creates a property literally named "key", not "a"
+// So the result is { key: 1 }.
+// Answer: { key: 1 }
 
 // b) What is the current return value when invert is called with { a: 1, b: 2 }
+// Object.entries({ a: 1, b: 2 }) → [["a", 1], ["b", 2]]
+// First loop: invertedObj.key = 1 → { key: 1 }
+// Second loop: invertedObj.key = 2 → overwrites previous value
+// Final result: { key: 2 }
+// Answer: { key: 2 }
 
 // c) What is the target return value when invert is called with {a : 1, b: 2}
+// { "1": "a", "2": "b" }
+// The goal is to swap keys and values, so keys become values and values become keys
 
 // c) What does Object.entries return? Why is it needed in this program?
+// Object.entries(obj) returns an array of [key, value] pairs from the object
+// Object.entries({ a: 1, b: 2 });
+// returns [["a", 1], ["b", 2]]
+// It’s needed so that the loop:
+// for (const [key, value] of Object.entries(obj))
+// can easily access both the key and value in one step.
 
 // d) Explain why the current return value is different from the target output
+// The current code uses invertedObj.key = value, which creates a property literally named "key".
+// To use the variable key dynamically, you must use bracket notation:
+// invertedObj[value] = key;
 
 // e) Fix the implementation of invert (and write tests to prove it's fixed!)
+
+function invert(obj) {
+  const invertedObj = {};
+  for (const [key, value] of Object.entries(obj)) {
+    invertedObj[value] = key;
+  }
+  return invertedObj;
+}
+
+module.exports = invert;
+

From 106d47e68046fadb5faa0d3cbef0b12e9d5575c6 Mon Sep 17 00:00:00 2001
From: Khor Biel <khorkoak@gmail.com>
Date: Fri, 21 Nov 2025 18:30:20 +0000
Subject: [PATCH 2/4] fix(contains): fix object syntax and add edge case tests

---
 Sprint-2/implement/contains.js      |  6 +++---
 Sprint-2/implement/contains.test.js | 24 +++++++++++++++++++++++-
 2 files changed, 26 insertions(+), 4 deletions(-)

diff --git a/Sprint-2/implement/contains.js b/Sprint-2/implement/contains.js
index 0f9373e2f..504fdc413 100644
--- a/Sprint-2/implement/contains.js
+++ b/Sprint-2/implement/contains.js
@@ -1,11 +1,11 @@
 function contains(obj, key) {
-  // Check if the first argument is a valid object
-  if (typeof obj !== "object" || obj === null || Array.isArray(obj)) {
+
+  if (typeof obj !== "object" || obj === null) {
     return false;
   }
 
-  // Check if the key exists in the object
   return Object.prototype.hasOwnProperty.call(obj, key);
 }
 
 module.exports = contains;
+
diff --git a/Sprint-2/implement/contains.test.js b/Sprint-2/implement/contains.test.js
index d32c99356..13727ced0 100644
--- a/Sprint-2/implement/contains.test.js
+++ b/Sprint-2/implement/contains.test.js
@@ -17,6 +17,7 @@ as the object doesn't contains a key of 'c'
 // When passed an object and a property name
 // Then it should return true if the object contains the property, false otherwise
 
+
 // Given an empty object
 // When passed to contains
 // Then it should return false
@@ -24,7 +25,6 @@ test("contains on empty object returns false", () => {
   expect(contains({}, "a")).toBe(false);
 });
 
-
 // Given an object with properties
 // When passed to contains with an existing property name
 // Then it should return true
@@ -45,3 +45,25 @@ test("contains on object with non-existent property returns false", () => {
 test("contains on invalid parameters returns false", () => {
   expect(contains([], "a")).toBe(false);
 });
+
+// === NEW TESTS ADDED BELOW ===
+
+// Test for inherited properties (should return false)
+test("contains should return false for inherited properties", () => {
+  expect(contains({a: 1, b: 2}, 'toString')).toBe(false);
+});
+
+// Test with arrays (should work properly)
+test("contains should work with arrays", () => {
+  expect(contains(['a', 'b', 'c'], '0')).toBe(true);
+  expect(contains(['a', 'b', 'c'], '1')).toBe(true); 
+  expect(contains(['a', 'b', 'c'], 'length')).toBe(false);
+});
+
+// Test with array as object
+test("contains should handle arrays correctly", () => {
+  const arr = ['x', 'y', 'z'];
+  expect(contains(arr, '0')).toBe(true);
+  expect(contains(arr, '2')).toBe(true);
+  expect(contains(arr, '3')).toBe(false);
+});
\ No newline at end of file

From 683286485c5fb4d587ae740342e4029c5319ae17 Mon Sep 17 00:00:00 2001
From: Khor Biel <khorkoak@gmail.com>
Date: Fri, 21 Nov 2025 18:54:45 +0000
Subject: [PATCH 3/4] fix(tally): use Object.create(null) to avoid inherited
 properties

---
 Sprint-2/implement/tally.js | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/Sprint-2/implement/tally.js b/Sprint-2/implement/tally.js
index 885a33825..91b726034 100644
--- a/Sprint-2/implement/tally.js
+++ b/Sprint-2/implement/tally.js
@@ -1,13 +1,12 @@
 function tally(items) {
-  // Validate input
+  
   if (!Array.isArray(items)) {
     throw new Error("Input must be an array");
   }
 
-  // Start with an empty object
-  const result = {};
+  const result = Object.create(null);
 
-  // Loop through the array and count
+  
   for (const item of items) {
     if (result[item]) {
       result[item] += 1;
@@ -17,6 +16,7 @@ function tally(items) {
   }
 
   return result;
+
 }
 
 module.exports = tally;

From e76a105cdd8fda5c75e7109e630530dac100c38c Mon Sep 17 00:00:00 2001
From: Khor Biel <khorkoak@gmail.com>
Date: Fri, 21 Nov 2025 19:27:06 +0000
Subject: [PATCH 4/4] `fix: correct contains.test.js array tests to properly
 check non-existing indices instead of length property`

---
 Sprint-2/implement/contains.js      |  4 ++--
 Sprint-2/implement/contains.test.js |  8 ++++---
 Sprint-2/stretch/count-words.js     | 36 +++++++++++++++++++++++++++++
 3 files changed, 43 insertions(+), 5 deletions(-)

diff --git a/Sprint-2/implement/contains.js b/Sprint-2/implement/contains.js
index 504fdc413..689b70b9b 100644
--- a/Sprint-2/implement/contains.js
+++ b/Sprint-2/implement/contains.js
@@ -1,11 +1,11 @@
 function contains(obj, key) {
-
+  // Check if the first argument is a valid object
   if (typeof obj !== "object" || obj === null) {
     return false;
   }
 
+  // Check if the key exists in the object (only own properties)
   return Object.prototype.hasOwnProperty.call(obj, key);
 }
 
 module.exports = contains;
-
diff --git a/Sprint-2/implement/contains.test.js b/Sprint-2/implement/contains.test.js
index 13727ced0..7925af3ab 100644
--- a/Sprint-2/implement/contains.test.js
+++ b/Sprint-2/implement/contains.test.js
@@ -55,11 +55,13 @@ test("contains should return false for inherited properties", () => {
 
 // Test with arrays (should work properly)
 test("contains should work with arrays", () => {
-  expect(contains(['a', 'b', 'c'], '0')).toBe(true);
-  expect(contains(['a', 'b', 'c'], '1')).toBe(true); 
-  expect(contains(['a', 'b', 'c'], 'length')).toBe(false);
+  expect(contains(["a", "b", "c"], "0")).toBe(true);
+  expect(contains(["a", "b", "c"], "1")).toBe(true);
+  expect(contains(["a", "b", "c"], "2")).toBe(true);
+  expect(contains(["a", "b", "c"], "3")).toBe(false); // check index that does not exist
 });
 
+
 // Test with array as object
 test("contains should handle arrays correctly", () => {
   const arr = ['x', 'y', 'z'];
diff --git a/Sprint-2/stretch/count-words.js b/Sprint-2/stretch/count-words.js
index 8e85d19d7..b1f445d7c 100644
--- a/Sprint-2/stretch/count-words.js
+++ b/Sprint-2/stretch/count-words.js
@@ -26,3 +26,39 @@
 
 3. Order the results to find out which word is the most common in the input
 */
+
+
+
+function countWords(str) {
+  // Use Object.create(null) to avoid inherited properties
+  const wordCounts = Object.create(null);
+
+  if (!str || str.trim() === "") {
+    return wordCounts;
+  }
+
+  // Split into words and handle punctuation/case
+  const words = str.split(/\s+/);
+
+  for (const word of words) {
+    // Remove punctuation and convert to lowercase
+    const cleanWord = word
+      .toLowerCase()
+      .replace(/[.,!?]/g, "")
+      .trim();
+
+    // Skip empty strings
+    if (cleanWord === "") continue;
+
+    // Count the word
+    if (wordCounts[cleanWord]) {
+      wordCounts[cleanWord] += 1;
+    } else {
+      wordCounts[cleanWord] = 1;
+    }
+  }
+
+  return wordCounts;
+}
+
+module.exports = countWords;
\ No newline at end of file