Cape Town| 26-ITP-May | Liyema Mfengwana| Sprint 2 | Data Groups

Sprint-2/debug/address.js

@@ -1,5 +1,5 @@
 // Predict and explain first...
-
+// it will log out the houseNumber from the address object, but it isn't working because the property name is incorrect. The correct property name is "houseNumber", not "houseNum".
 // This code should log out the houseNumber from the address object
 // but it isn't working...
 // Fix anything that isn't working
@@ -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}`);

Sprint-2/debug/author.js

@@ -1,7 +1,10 @@
 // Predict and explain first...
 
+//You’ll get an error
+
 // 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 for...of loop is used to iterate over iterable objects like arrays, strings, etc.
 
 const author = {
   firstName: "Zadie",
@@ -11,6 +14,6 @@ const author = {
   alive: true,
 };
 
-for (const value of author) {
+for (const value of Object.values(author)) {
   console.log(value);
 }

Sprint-2/debug/recipe.js

@@ -1,5 +1,6 @@
 // Predict and explain first...
-
+//Prediction: The program will print the recipe title and number of servings, but instead of printing the ingredients, it will display [object Object].
+//recipe is the whole object, so JavaScript will convert it to: object Object
 // 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?
@@ -11,5 +12,8 @@ const recipe = {
 };
 
 console.log(`${recipe.title} serves ${recipe.serves}
-  ingredients:
-${recipe}`);
+ ingredients:`);
+
+for (const ingredient of recipe.ingredients) {
+  console.log(ingredient);
+}

Sprint-2/implement/contains.js

@@ -1,3 +1,8 @@
-function contains() {}
+function contains(object, propertyName) {
+  if (object === null || typeof object !== "object" || Array.isArray(object)) {
+    return false;
+  }
 
+  return Object.hasOwn(object, propertyName);
+}
 module.exports = contains;

Sprint-2/implement/contains.test.js

@@ -20,16 +20,27 @@ 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 an empty object returns false", () => {
+  expect(contains({}, "propertyName")).toBe(false);
+});
 
 // Given an object with properties
 // When passed to contains with an existing property name
 // Then it should return true
+test("returns true when the property exists", () => {
+  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("returns false when the property doesn't exist", () => {
+  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("returns false for invalid input types", () => {
+  expect(contains([1, 2, 3], "0")).toBe(false);
+});

Sprint-2/implement/lookup.js

@@ -1,5 +1,11 @@
-function createLookup() {
-  // implementation here
+function createLookup(countryCurrencyPairs) {
+  const lookup = {};
+
+  for (const [countryCode, currencyCode] of countryCurrencyPairs) {
+    lookup[countryCode] = currencyCode;
+  }
+
+  return lookup;
 }
 
 module.exports = createLookup;

Sprint-2/implement/lookup.test.js

@@ -1,7 +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"],
+  ];
+
+  expect(createLookup(countryCurrencyPairs)).toEqual({
+    US: "USD",
+    CA: "CAD",
+  });
+});
 /*
 
 Create a lookup object of key value pairs from an array of code pairs

Sprint-2/implement/querystring.js

@@ -6,10 +6,29 @@ function parseQueryString(queryString) {
   const keyValuePairs = queryString.split("&");
 
   for (const pair of keyValuePairs) {
-    const [key, value] = pair.split("=");
-    queryParams[key] = value;
-  }
+    if (pair === "") {
+      continue;
+    }
+
+    const separatorIndex = pair.indexOf("=");
+
+    const encodedKey =
+      separatorIndex === -1 ? pair : pair.slice(0, separatorIndex);
 
+    const encodedValue =
+      separatorIndex === -1 ? "" : pair.slice(separatorIndex + 1);
+
+    const key = decodeURIComponent(encodedKey.replaceAll("+", " "));
+    const value = decodeURIComponent(encodedValue.replaceAll("+", " "));
+
+    if (!Object.hasOwn(queryParams, key)) {
+      queryParams[key] = value;
+    } else if (Array.isArray(queryParams[key])) {
+      queryParams[key].push(value);
+    } else {
+      queryParams[key] = [queryParams[key], value];
+    }
+  }
   return queryParams;
 }
 

Sprint-2/implement/tally.js

@@ -1,3 +1,14 @@
-function tally() {}
+function tally(items) {
+  if (!Array.isArray(items)) {
+    throw new TypeError("Expected an array");
+  }
+  const counts = Object.create(null);
+
+  for (const item of items) {
+    counts[item] = (counts[item] || 0) + 1;
+  }
+
+  return counts;
+}
 
 module.exports = tally;

Sprint-2/implement/tally.test.js

@@ -23,7 +23,21 @@ 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({});
+});
+
+test("returns the count for each unique item", () => {
+  expect(tally(["a", "a", "b", "c"])).toEqual({
+    a: 2,
+    b: 1,
+    c: 1,
+  });
+});
+
+test("throws an error when passed a string", () => {
+  expect(() => tally("a, a, b")).toThrow(TypeError);
+});
 
 // Given an array with duplicate items
 // When passed to tally

Sprint-2/interpret/invert.js

@@ -10,20 +10,32 @@ function invert(obj) {
   const invertedObj = {};
 
   for (const [key, value] of Object.entries(obj)) {
-    invertedObj.key = value;
+    invertedObj[value] = key;
   }
 
   return invertedObj;
 }
 
 // a) What is the current return value when invert is called with { a : 1 }
+// a) Before the fix, invert({ a: 1 }) returned:
+// { key: 1 }
 
 // b) What is the current return value when invert is called with { a: 1, b: 2 }
+// b) Before the fix, invert({ a: 1, b: 2 }) returned:
+// { key: 2 }
+// The second loop replaced the first value.
 
 // c) What is the target return value when invert is called with {a : 1, b: 2}
+// c) The target return value is:
+// { "1": "a", "2": "b" }
 
 // c) What does Object.entries return? Why is it needed in this program?
+// d) Object.entries returns an array of [key, value] pairs.
+// It allows the loop to access both parts of each property.
 
 // d) Explain why the current return value is different from the target output
+// e) The original code used dot notation, which created a property
+// literally named "key" instead of using the value dynamically.
 
 // e) Fix the implementation of invert (and write tests to prove it's fixed!)
+module.exports = invert;

Sprint-2/interpret/invert.test.js

@@ -0,0 +1,12 @@
+const invert = require("./invert.js");
+
+test("swaps the keys and values in an object", () => {
+  expect(invert({ a: 1, b: 2 })).toEqual({
+    1: "a",
+    2: "b",
+  });
+});
+
+test("returns an empty object for an empty object", () => {
+  expect(invert({})).toEqual({});
+});

Sprint-2/stretch/count-words.js

@@ -26,3 +26,18 @@
 
 3. Order the results to find out which word is the most common in the input
 */
+function countWords(text) {
+  const cleanedText = text.toLowerCase().replace(/[.,!?]/g, "");
+
+  const words = cleanedText.split(" ").filter((word) => word !== "");
+
+  const wordCounts = {};
+
+  for (const word of words) {
+    wordCounts[word] = (wordCounts[word] || 0) + 1;
+  }
+
+  return wordCounts;
+}
+
+module.exports = countWords;

Sprint-2/stretch/mode.js

@@ -8,22 +8,25 @@
 // refactor calculateMode by splitting up the code
 // into smaller functions using the stages above
 
-function calculateMode(list) {
-  // track frequency of each value
-  let freqs = new Map();
+function countFrequencies(list) {
+  const freqs = new Map();
 
-  for (let num of list) {
+  for (const num of list) {
     if (typeof num !== "number") {
       continue;
     }
 
     freqs.set(num, (freqs.get(num) || 0) + 1);
   }
 
-  // Find the value with the highest frequency
+  return freqs;
+}
+
+function findHighestFrequency(frequencies) {
   let maxFreq = 0;
   let mode;
-  for (let [num, freq] of freqs) {
+
+  for (const [num, freq] of frequencies) {
     if (freq > maxFreq) {
       mode = num;
       maxFreq = freq;
@@ -33,4 +36,9 @@ function calculateMode(list) {
   return maxFreq === 0 ? NaN : mode;
 }
 
+function calculateMode(list) {
+  const frequencies = countFrequencies(list);
+  return findHighestFrequency(frequencies);
+}
+
 module.exports = calculateMode;

Sprint-2/stretch/till.js

@@ -8,24 +8,23 @@ function totalTill(till) {
   let total = 0;
 
   for (const [coin, quantity] of Object.entries(till)) {
-    total += coin * quantity;
+    const coinValue = parseInt(coin, 10);
+    total += coinValue * quantity;
   }
 
   return `£${total / 100}`;
 }
 
-const till = {
-  "1p": 10,
-  "5p": 6,
-  "50p": 4,
-  "20p": 10,
-};
-const totalAmount = totalTill(till);
-
 // a) What is the target output when totalTill is called with the till object
+// a) The target output is £4.4
 
 // b) Why do we need to use Object.entries inside the for...of loop in this function?
+// b) Object.entries converts the object into key-value pairs,
+//    allowing us to access both the coin and its quantity.
 
 // c) What does coin * quantity evaluate to inside the for...of loop?
+// c) coinValue * quantity calculates the total value
+//    of that type of coin.
 
 // d) Write a test for this function to check it works and then fix the implementation of totalTill
+module.exports = totalTill;

Sprint-2/stretch/till.test.js

@@ -0,0 +1,16 @@
+const totalTill = require("./till.js");
+
+test("calculates the total amount in the till", () => {
+  const till = {
+    "1p": 10,
+    "5p": 6,
+    "50p": 4,
+    "20p": 10,
+  };
+
+  expect(totalTill(till)).toBe("£4.4");
+});
+
+test("returns £0 for an empty till", () => {
+  expect(totalTill({})).toBe("£0");
+});