London | ITP-May-2025 | Seddiq Azam | Module-Data-Groups | Sprint 2

Sprint-2/debug/address.js

@@ -4,6 +4,12 @@
 // but it isn't working...
 // Fix anything that isn't working
 
+// The code is trying to log the `houseNumber` property from the `address` object.
+// However, the `address` object is not defined in the provided code snippet.
+// To fix this, we need to define the `address` object first and then log the
+// `houseNumber` property correctly.
+// The code is also using a template literal to log the value, which is correct.
+// Let's define the `address` object and log the `houseNumber` property.
 const address = {
   houseNumber: 42,
   street: "Imaginary Road",
@@ -12,4 +18,4 @@ 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

@@ -1,5 +1,10 @@
 // Predict and explain first...
 
+// This code is trying to log out the values of the properties in the `author` object.
+// However, the `for...of` loop is designed to iterate over iterable objects like arrays
+// or strings, not over objects. Since `author` is an object, the loop will not work as intended,
+// and it will throw a TypeError because objects are not iterable by default.
+
 // 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 +16,10 @@ const author = {
   alive: true,
 };
 
-for (const value of author) {
+// The correct way to iterate over the values of an object is to use `Object.values()`
+// which returns an array of the object's values, and then use `for...of` to
+// iterate over that array.
+// Here is the corrected code:
+for (const value of Object.values(author)) {
   console.log(value);
 }

Sprint-2/debug/recipe.js

@@ -1,5 +1,10 @@
 // Predict and explain first...
 
+// This code is intended to log out a recipe object in a specific format.
+// However, it currently does not log the ingredients correctly.
+// The issue is that it tries to log the entire recipe object directly, which will not format the ingredients as intended.
+// Instead, it should iterate over the ingredients array and log each ingredient on a new line.
+
 // 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?
@@ -12,4 +17,4 @@ const recipe = {
 
 console.log(`${recipe.title} serves ${recipe.serves}
   ingredients:
-${recipe}`);
+${recipe.ingredients.join("\n")}`);

Sprint-2/implement/contains.js

@@ -1,3 +1,11 @@
-function contains() {}
+function contains(obj, property) {
+  // Safety check: handle invalid inputs
+  if (typeof obj !== "object" || obj === null || Array.isArray(obj)) {
+    return false; // Return false for non-object types, null, undefined, or arrays
+  }
+
+  // Check if the object has the specified property
+  return obj.hasOwnProperty(property); // Use hasOwnProperty to check for the property
+}
 
 module.exports = contains;

Sprint-2/implement/contains.test.js

@@ -17,19 +17,42 @@ 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
 
+test("contains a property in an object should return true or false", () => {
+  expect(contains({ a: 1, b: 2 }, "a")).toBe(true);
+  expect(contains({ a: 1, b: 2 }, "b")).toBe(true);
+  expect(contains({ a: 1, b: 2 }, "c")).toBe(false);
+});
+
 // Given an empty object
 // When passed to contains
 // Then it should return false
-test.todo("contains on empty object returns false");
+test("contains an empty object should return 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 an existing property in an object should return true", () => {
+  expect(contains({ a: 1, b: 2 }, "a")).toBe(true);
+  expect(contains({ a: 1, b: 2 }, "b")).toBe(true);
+});
+
 // Given an object with properties
 // When passed to contains with a non-existent property name
 // Then it should return false
 
+test("contains a non-existent property in an object should return 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 with invalid parameters should return false", () => {
+  expect(contains(null, "a")).toBe(false);
+  expect(contains(undefined, "a")).toBe(false);
+  expect(contains([], "a")).toBe(false);
+  expect(contains("string", "a")).toBe(false);
+});

Sprint-2/implement/lookup.js

@@ -1,5 +1,21 @@
-function createLookup() {
-  // implementation here
+function createLookup(countryCurrencyPairs) {
+  const result = {};
+
+  for (let i = 0; i < countryCurrencyPairs.length; i++) {
+    const pair = countryCurrencyPairs[i];
+    const [countryCode, currencyCode] = pair;
+
+    result[countryCode] = currencyCode;
+  }
+
+  return result;
 }
 
+console.log(
+  createLookup([
+    ["US", "USD"],
+    ["CA", "CAD"],
+  ])
+);
+
 module.exports = createLookup;

Sprint-2/implement/lookup.test.js

@@ -1,7 +1,5 @@
 const createLookup = require("./lookup.js");
 
-test.todo("creates a country currency code lookup for multiple codes");
-
 /*
 
 Create a lookup object of key value pairs from an array of code pairs
@@ -33,3 +31,14 @@ It should return:
    'CA': 'CAD'
  }
 */
+test("given an array of country-currency pairs, createLookup should return an object with country codes as keys and currency codes as values", () => {
+  expect(
+    createLookup([
+      ["US", "USD"],
+      ["CA", "CAD"],
+    ])
+  ).toEqual({
+    US: "USD",
+    CA: "CAD",
+  });
+});

Sprint-2/implement/querystring.js

@@ -5,12 +5,21 @@ function parseQueryString(queryString) {
   }
   const keyValuePairs = queryString.split("&");
 
-  for (const pair of keyValuePairs) {
-    const [key, value] = pair.split("=");
-    queryParams[key] = value;
+  for (let i = 0; i < keyValuePairs.length; i++) {
+    const pair = keyValuePairs[i];
+    const firstEqualIndex = pair.indexOf("=");
+
+    if (firstEqualIndex === -1) {
+      // If there is no equal sign, treat the whole pair as a key with an empty value
+      queryParams[pair] = "";
+    } else {
+      const key = pair.slice(0, firstEqualIndex);
+      const value = pair.slice(firstEqualIndex + 1);
+      queryParams[key] = value;
+    }
   }
 
   return queryParams;
 }
-
+console.log(parseQueryString("equation=x=y+1")); // { equation: 'x=y+1' }
 module.exports = parseQueryString;

Sprint-2/implement/querystring.test.js

@@ -3,10 +3,14 @@
 // Below is one test case for an edge case the implementation doesn't handle well.
 // Fix the implementation for this test, and try to think of as many other edge cases as possible - write tests and fix those too.
 
-const parseQueryString = require("./querystring.js")
+const parseQueryString = require("./querystring.js");
 
 test("parses querystring values containing =", () => {
   expect(parseQueryString("equation=x=y+1")).toEqual({
-    "equation": "x=y+1",
+    equation: "x=y+1",
   });
 });
+
+test("parses querystring with no values", () => {
+  expect(parseQueryString("")).toEqual({});
+});

Sprint-2/implement/tally.js

@@ -1,3 +1,18 @@
-function tally() {}
+function tally(inputArray) {
+  if (!Array.isArray(inputArray)) {
+    throw new Error("Input must be an array");
+  }
 
+  const result = Object.create(null);
+
+  for (const element of inputArray) {
+    if (result[element]) {
+      result[element] += 1;
+    } else {
+      result[element] = 1;
+    }
+  }
+  return result;
+}
+console.log(tally(["toString", "toString", "toString"]));
 module.exports = tally;

Sprint-2/implement/tally.test.js

@@ -19,16 +19,32 @@ 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 should return an object with counts for each unique item", () => {
+  const input = ["a", "b", "a", "c"];
+  const expectedOutput = { a: 2, b: 1, c: 1 };
+  expect(tally(input)).toEqual(expectedOutput);
+});
 
 // 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 should return an empty object for an empty array", () => {
+  expect(tally([])).toEqual({});
+});
 
 // Given an array with duplicate items
 // When passed to tally
 // Then it should return counts for each unique item
+test("tally should return counts for duplicate items", () => {
+  const input = ["a", "a", "b", "c"];
+  const expectedOutput = { a: 2, b: 1, c: 1 };
+  expect(tally(input)).toEqual(expectedOutput);
+});
 
 // Given an invalid input like a string
 // When passed to tally
 // Then it should throw an error
+
+test("tally should throw an error for invalid input", () => {
+  expect(() => tally("not an array")).toThrow("Input must be an array");
+});

Sprint-2/interpret/invert.js

@@ -10,20 +10,55 @@ function invert(obj) {
   const invertedObj = {};
 
   for (const [key, value] of Object.entries(obj)) {
-    invertedObj.key = value;
+    invertedObj[value] = key;
   }
 
   return invertedObj;
 }
 
+// Test cases to verify the functionality of invert
+console.log(invert({ a: 1 })); // { '1': 'a' }
+console.log(invert({ a: 1, b: 2 })); // { '1': 'a', '2': 'b' }
+console.log(invert({ x: 10, y: 20 })); // { '10': 'x', '20': 'y' }
+console.log(invert({ name: "Alice", age: 30 })); // { 'Alice': 'name', '30': 'age' }
+
 // a) What is the current return value when invert is called with { a : 1 }
 
+/* { key: 1 }. This is because the code is using `invertedObj.key`. 
+it uses dot notation with the literal word "key". 
+The key 'key' is being set to the value of 1.
+If we use `invertedObj.Smith = 1`, it will return { Smith: 1 }
+/*
+
 // b) What is the current return value when invert is called with { a: 1, b: 2 }
 
+/* { key: 2 }
+This is because the loop iterates over the entries of the object,
+and the last entry processed is 'b: 2'.
+The key 'key' is set to the value of 2, overwriting the previous value
+of 1 from the first iteration.
+*/
+
 // c) What is the target return value when invert is called with {a : 1, b: 2}
 
+/* { '1': 'a', '2': 'b' }
+This is the expected output where the keys and values are swapped.
+*/
+
 // c) What does Object.entries return? Why is it needed in this program?
 
+/* [["a", 1], ["b", 2]]
+Object.entries returns an array of key-value pairs from the object.
+It is needed in this program to iterate over the object's properties
+and their values, allowing us to swap them in 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 the code is incorrectly using `invertedObj.key` instead of using the variable `key` to set the property name dynamically.
+This means it always sets the property 'key' to the last value processed in the loop,
+instead of creating properties with the original values as keys and the original keys as values.
+*/
+
 // e) Fix the implementation of invert (and write tests to prove it's fixed!)

Sprint-2/stretch/count-words.js

@@ -26,3 +26,34 @@
 
 3. Order the results to find out which word is the most common in the input
 */
+
+const countWords = (str) => {
+  if (str.trim().length === 0) {
+    return 0;
+  }
+  const words = str.split(" ");
+  const counts = Object.create(null);
+
+  for (const eachWord of words) {
+    if (eachWord in counts) {
+      counts[eachWord]++;
+    } else {
+      counts[eachWord] = 1;
+    }
+  }
+
+  return counts;
+};
+
+console.log(countWords("you and me and you")); // { you: 2, and: 2, me: 1 }
+console.log(countWords("hello world hello")); // { hello: 2, world: 1 }
+console.log(countWords("this is a test this is only a test")); // { this: 2, is: 2, a: 2, test: 2, only: 1 }
+console.log(countWords("")); // 0
+console.log(countWords("   ")); // 0
+console.log(countWords("one two three one two")); // { one: 2, two: 2, three: 1 }
+console.log(countWords("apple banana apple orange banana apple")); // { apple: 3, banana: 2, orange: 1 }
+console.log(countWords("The quick brown fox jumps over the lazy dog")); // { The: 1, quick: 1, brown: 1, fox: 1, jumps: 1,
+// over: 1, the: 1, lazy: 1, dog: 1 }
+
+console.log(countWords("0 1 2 3 4 5 6 6 6 6 7 7 7 7 7 7 8 9 9 9 0 0")); // { '0': 2, '1': 1, '2': 1, '3': 1, '4': 1, '5': 1, '6': 1, '7': 1, '8': 1, '9': 1 }
+console.log(JSON.stringify(countWords("constructor constructor constructor"))); // { constructor: 3 }

Sprint-2/stretch/mode.js

@@ -8,22 +8,26 @@
 // refactor calculateMode by splitting up the code
 // into smaller functions using the stages above
 
-function calculateMode(list) {
+function getFrequencies(list) {
   // track frequency of each value
-  let freqs = new Map();
+  const frequencies = new Map();
 
   for (let num of list) {
     if (typeof num !== "number") {
       continue;
     }
 
-    freqs.set(num, (freqs.get(num) || 0) + 1);
+    frequencies.set(num, (frequencies.get(num) || 0) + 1);
   }
+  return frequencies;
+}
 
-  // Find the value with the highest frequency
+// Find the value with the highest frequency
+function getMostFrequentValue(frequencies) {
   let maxFreq = 0;
   let mode;
-  for (let [num, freq] of freqs) {
+
+  for (let [num, freq] of frequencies) {
     if (freq > maxFreq) {
       mode = num;
       maxFreq = freq;
@@ -33,4 +37,11 @@ function calculateMode(list) {
   return maxFreq === 0 ? NaN : mode;
 }
 
+function calculateMode(list) {
+  const frequencies = getFrequencies(list);
+  return getMostFrequentValue(frequencies);
+}
+
+console.log(calculateMode([1, 2, 2, 3, 4, 4, 4, 5])); // Output: 4
+console.log(calculateMode([1, 1, 2, "2", 3, 3])); // Output: 1 (or 2 or 3, since they
 module.exports = calculateMode;