London | ITP-JAN-2026 | Said Fayaz Sadat | Sprint 2 | coursework/sprint 2

Sprint-2/debug/address.js

@@ -1,4 +1,7 @@
 // Predict and explain first...
+// The code is trying to access the houseNumber property of the address object using an index, which is not correct.
+// In JavaScript, objects are accessed using their property names, not indices. 
+// To fix this, we should use the property name 'houseNumber' instead of an index.
 
 // This code should log out the houseNumber from the address object
 // but it isn't working...
@@ -12,4 +15,4 @@ const address = {
   postcode: "XYZ 123",
 };
 
-console.log(`My house number is ${address[0]}`);
+console.log(`My house number is ${address.houseNumber}`);

Sprint-2/debug/author.js

@@ -2,6 +2,8 @@
 
 // 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
+// The code is trying to iterate over the properties of the author object using a for...of loop, which is not correct for objects in JavaScript.
+// In JavaScript, objects are not iterable with for...of loops. Instead, we can use a for...in loop to iterate over the property names of the object, and then access the corresponding values.
 
 const author = {
   firstName: "Zadie",
@@ -11,6 +13,6 @@ const author = {
   alive: true,
 };
 
-for (const value of author) {
-  console.log(value);
-}
+for (const key in author) {
+  console.log(author[key]); 
+}

Sprint-2/debug/recipe.js

@@ -3,6 +3,10 @@
 // This program should log out the title, how many it serves and the ingredients.
 // Each ingredient should be logged on a new line
 // How can you fix it?
+/* The issue with the code is that it is trying to log the entire recipe object directly, which will not format the ingredients as desired. 
+Instead, we need to access the properties of the recipe object and format the output correctly. 
+We can use template literals to format the string and join the ingredients array with new line characters.
+*/
 
 const recipe = {
   title: "bruschetta",
@@ -12,4 +16,4 @@ const recipe = {
 
 console.log(`${recipe.title} serves ${recipe.serves}
   ingredients:
-${recipe}`);
+${recipe.ingredients.join('\n')}`);

Sprint-2/implement/contains.js

@@ -1,3 +1,9 @@
-function contains() {}
+function contains(obj, key) {
+  if (obj === null || typeof obj !== "object" || Array.isArray(obj)) {
+    return false;
+  }
+
+  return Object.hasOwn(obj, key);
+}
 
-module.exports = contains;
+module.exports = contains;

Sprint-2/implement/contains.test.js

@@ -16,20 +16,44 @@ as the object doesn't contains a key of 'c'
 // Given a contains function
 // When passed an object and a property name
 // Then it should return true if the object contains the property, false otherwise
+test("returns true if the object contains the property, false otherwise", () => {
+  const obj = { a: 1, b: 2 };
+
+  expect(contains(obj, "a")).toBe(true);   // existing property
+  expect(contains(obj, "b")).toBe(true);   // existing property
+  expect(contains(obj, "c")).toBe(false);  // non‑existent property
+});
+
+
 
 // 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", () => {
+  // We use an index that EXISTS in the array (0)
+  // If the function returns false, we know it's because it rejected the ARRAY type
+  expect(contains(["test"], 0)).toBe(false);
+  expect(contains(null, "a")).toBe(false);
+});

Sprint-2/implement/lookup.js

@@ -1,5 +1,11 @@
-function createLookup() {
-  // implementation here
+function createLookup(countryCurrencyPairs) {
+  let lookup = {};
+  for (let pair of countryCurrencyPairs) {
+    let key = pair[0];
+    let value = pair[1];
+    lookup[key] = value;
+  }
+  return lookup;
 }
 
 module.exports = createLookup;

Sprint-2/implement/lookup.test.js

@@ -1,6 +1,16 @@
 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", () => {
+  const countryCurrencyPairs = [['US', 'USD'], ['CA', 'CAD'], ['GB', 'GBP']];
+  const expectedLookup = {
+    US: 'USD',
+    CA: 'CAD',
+    GB: 'GBP'
+  };
+
+  expect(createLookup(countryCurrencyPairs)).toEqual(expectedLookup);
+});
+
 
 /*
 

Sprint-2/implement/querystring.js

@@ -1,16 +1,30 @@
 function parseQueryString(queryString) {
   const queryParams = {};
+
   if (queryString.length === 0) {
     return queryParams;
   }
+
   const keyValuePairs = queryString.split("&");
 
   for (const pair of keyValuePairs) {
-    const [key, value] = pair.split("=");
+    const index = pair.indexOf("=");
+
+    let key;
+    let value;
+
+    if (index === -1) {
+      key = pair;
+      value = "";
+    } else {
+      key = pair.slice(0, index);
+      value = pair.slice(index + 1);
+    }
+
     queryParams[key] = value;
   }
 
   return queryParams;
 }
 
-module.exports = parseQueryString;
+module.exports = parseQueryString;

Sprint-2/implement/querystring.test.js

@@ -10,3 +10,28 @@ test("parses querystring values containing =", () => {
     "equation": "x=y+1",
   });
 });
+
+test("parses querystring values containing &", () => {
+  expect(parseQueryString("equation=x&y=1")).toEqual({
+    "equation": "x",
+    "y": "1",
+  });
+});
+
+test("parses querystring values containing & and =", () => {
+  expect(parseQueryString("equation=x&y=1&formula=a=b+c")).toEqual({
+    "equation": "x",
+    "y": "1",
+    "formula": "a=b+c",
+  });
+});
+
+test("parses empty querystring", () => {
+  expect(parseQueryString("")).toEqual({});
+});
+
+test("parses querystring with no value", () => {
+  expect(parseQueryString("key")).toEqual({
+    "key": "",
+  });
+});   

Sprint-2/implement/tally.js

@@ -1,3 +1,19 @@
-function tally() {}
+function tally(items) {
+  if (!Array.isArray(items)) {
+    throw new Error("Input must be an array");
+  }
 
-module.exports = tally;
+  const result = Object.create(null);
+
+  for (const item of items) {
+    if (result[item]) {
+      result[item]++;
+    } else {
+      result[item] = 1;
+    }
+  }
+
+  return result;
+}
+
+module.exports = tally;

Sprint-2/implement/tally.test.js

@@ -19,16 +19,29 @@ const tally = require("./tally.js");
 // Given a function called tally
 // When passed an array of items
 // Then it should return an object containing the count for each unique item
+test("tally counts the frequency of each item 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 });
+});
 
 // 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("tally counts duplicate items correctly", () => {
+  expect(tally(["x", "y", "x", "z", "y"])).toEqual({ x: 2, y: 2, z: 1 });
+});
 
 // Given an invalid input like a string
 // When passed to tally
 // Then it should throw an error
+test("tally throws an error for non-array input", () => {
+  expect(() => tally("not an array")).toThrow("Input must be an array");
+});

Sprint-2/interpret/invert.js

@@ -6,7 +6,7 @@
 
 // E.g. invert({x : 10, y : 20}), target output: {"10": "x", "20": "y"}
 
-function invert(obj) {
+/* function invert(obj) {
   const invertedObj = {};
 
   for (const [key, value] of Object.entries(obj)) {
@@ -15,15 +15,42 @@ function invert(obj) {
 
   return invertedObj;
 }
+  */
 
 // a) What is the current return value when invert is called with { a : 1 }
+// the current return value is { key: 1 }
 
 // b) What is the current return value when invert is called with { a: 1, b: 2 }
+// the current return value is { key: 1, key: 2 }
 
 // c) What is the target return value when invert is called with {a : 1, b: 2}
+// the target return value is { "1": "a", "2": "b" }
 
 // c) What does Object.entries return? Why is it needed in this program?
+/* Object.entries returns an array of a given object's own enumerable string-keyed property [key, value] pairs.
+In this program, it is needed to iterate over the key-value pairs of the input object so that we can swap them and create the inverted object.
+*/
 
 // d) Explain why the current return value is different from the target output
+/* The current return value is different from the target output because in the current implementation,
+ we are assigning the value to a property named "key" in the inverted object,
+  which means that every key-value pair in the input object will overwrite the same "key" property in the inverted object.
+  As a result, only the last key-value pair from the input object will be reflected in the inverted object, leading to incorrect output.
+  To achieve the target output, we need to use the value from the input object as the key in the inverted object and 
+  the key from the input object as the value in the inverted object.
+*/
 
 // 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;
+}
+
+
+
+expect(invert({ a: 1, b: 2 })).toEqual({ '1': 'a', '2': 'b' });