ZA | May-2025 | Malusi Skunyana | Sprint-2

Sprint-2/debug/address.js

@@ -1,7 +1,13 @@
 // Predict and explain first...
+// The code is trying to access the houseNumber property of the address object
+// but it's using an incorrect syntax. Instead of using address[0],
+// it should use address.houseNumber or address['houseNumber'].
 
 // This code should log out the houseNumber from the address object
 // but it isn't working...
+// It logs `undefined` because `address[0]` is trying to access the first element 
+// of an array, but `address` is an object, not an array.
+
 // Fix anything that isn't working
 
 const address = {
@@ -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

@@ -1,7 +1,14 @@
 // Predict and explain first...
+// The code is trying to iterate over the `author` object using a `for...of` loop.
+// However, `for...of` is designed to iterate over iterable objects like arrays or 
+// strings and does not work with plain objects. Therefore, it will throw a `TypeError`
+// indicating that the object is 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
+// It isn't working because the `for...of` loop is not suitable for iterating over
+// an object. Instead, we can use `Object.values()` to get an array of the
+// object's values and then iterate over that array. 
 
 const author = {
   firstName: "Zadie",
@@ -11,6 +18,6 @@ const author = {
   alive: true,
 };
 
-for (const value of author) {
+for (const value of Object.values(author)) {
   console.log(value);
 }

Sprint-2/debug/recipe.js

@@ -1,8 +1,16 @@
 // Predict and explain first...
+// The code will log out the title and how many it serves, but it will not log 
+// the ingredients correctly. It will not log ingredients correctly because 
+// ${recipe} does not access the ingredients array properly. Secondly, it will 
+// not format the ingredients on new lines as expected.
 
 // 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?
+// To fix it, we need to access the ingredients array properly and format it so 
+// that each ingredient appears on a new line. We can use the join method to 
+// convert the array into a string with each ingredient on a new line and use 
+// template literals to format the output correctly. 
 
 const recipe = {
   title: "bruschetta",
@@ -11,5 +19,5 @@ const recipe = {
 };
 
 console.log(`${recipe.title} serves ${recipe.serves}
-  ingredients:
-${recipe}`);
+ingredients:
+  ${recipe.ingredients.join('\n  ')}`);

Sprint-2/implement/contains.js

@@ -1,3 +1,21 @@
-function contains() {}
+function contains() {
+    // Check if the first argument is an object
+    if (typeof arguments[0] !== 'object' || arguments[0] === null) {
+        return false; // Return false for non-object types
+    }
+
+    // If the first argument is an array, return false
+    if (Array.isArray(arguments[0])) {
+        return false;
+    }
+
+    // Check if the second argument is a string
+    if (typeof arguments[1] !== 'string') {
+        return false; // Return false for non-string property names
+    }
+
+    // Check if the object contains the property
+    return Object.prototype.hasOwnProperty.call(arguments[0], arguments[1]);
+}
 
 module.exports = contains;

Sprint-2/implement/contains.test.js

@@ -16,20 +16,38 @@ 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("contains on object with existing property returns true", () => {
+  expect(contains({ a: 1, b: 2 }, 'a')).toBe(true);
+});
+
+test("contains on object with non-existent property returns false", () => {
+  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 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 array returns false", () => {
+  expect(contains([1, 2, 3], '0')).toBe(false);
+});

Sprint-2/implement/lookup.js

@@ -1,5 +1,9 @@
-function createLookup() {
-  // implementation here
+function createLookup(pairs) {
+  const lookup = {};
+  for (const [country, currency] of pairs) {
+    lookup[country] = currency;
+  }
+  return lookup;
 }
 
 module.exports = createLookup;

Sprint-2/implement/lookup.test.js

@@ -1,6 +1,13 @@
 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 input = [['US', 'USD'], ['CA', 'CAD']];
+  const expectedOutput = {
+    US: 'USD',
+    CA: 'CAD'
+  };
+  expect(createLookup(input)).toEqual(expectedOutput);
+});
 
 /*
 

Sprint-2/implement/querystring.js

@@ -6,8 +6,12 @@ function parseQueryString(queryString) {
   const keyValuePairs = queryString.split("&");
 
   for (const pair of keyValuePairs) {
-    const [key, value] = pair.split("=");
-    queryParams[key] = value;
+    const [key, ...rest] = pair.split("=");
+    const value = rest.join("=");
+    // Decode key and value to handle special characters
+    const decodedKey = decodeURIComponent(key);
+    const decodedValue = decodeURIComponent(value);
+    queryParams[decodedKey] = decodedValue;
   }
 
   return queryParams;

Sprint-2/implement/querystring.test.js

@@ -10,3 +10,45 @@ test("parses querystring values containing =", () => {
     "equation": "x=y+1",
   });
 });
+
+test("parses querystring values containing multiple =", () => {
+  expect(parseQueryString("equation=x=y+1&another=2=3")).toEqual({
+    "equation": "x=y+1",
+    "another": "2=3",
+  });
+});
+
+test("parses querystring with no values", () => {
+  expect(parseQueryString("")).toEqual({});
+});
+
+test("parses querystring with multiple values", () => {
+  expect(parseQueryString("a=1&b=2&c=3")).toEqual({
+    "a": "1",
+    "b": "2",
+    "c": "3",
+  });
+});
+
+test("parses querystring with empty values", () => {
+  expect(parseQueryString("a=&b=&c=")).toEqual({
+    "a": "",
+    "b": "",
+    "c": "",
+  });
+});
+
+test("parses querystring with special characters", () => {
+  expect(parseQueryString("a=1&b=2%20with%20spaces&c=3%40email.com")).toEqual({
+    "a": "1",
+    "b": "2 with spaces",
+    "c": "3@email.com",
+  });
+});
+
+test("parses querystring with encoded characters", () => {
+  expect(parseQueryString("a=1&b=%C3%A9%20%C3%A0%20%C3%A9")).toEqual({
+    "a": "1",
+    "b": "é à é",
+  });
+});

Sprint-2/implement/tally.js

@@ -1,3 +1,15 @@
-function tally() {}
+function tally(items) {
+    if (!Array.isArray(items)) {
+        throw new Error("Invalid input");
+    }
+
+    return items.reduce((acc, item) => {
+        if (typeof item !== 'string') {
+            throw new Error("Invalid input");
+        }
+        acc[item] = (acc[item] || 0) + 1;
+        return acc;
+    }, {});
+}
 
 module.exports = tally;

Sprint-2/implement/tally.test.js

@@ -19,16 +19,36 @@ 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 on an array of items returns an object with counts", () => {
+  const input = ['a', 'b', 'a', 'c', 'b', 'a'];
+  const expectedOutput = { a: 3, b: 2, c: 1 };
+  const result = tally(input);
+  expect(result).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 on an empty array returns an empty object", () => {
+  const input = [];
+  const expectedOutput = {};
+  const result = tally(input);
+  expect(result).toEqual(expectedOutput);
+});
 
 // Given an array with duplicate items
 // When passed to tally
 // Then it should return counts for each unique item
+test("tally on an array with duplicate items returns counts for each unique item", () => {
+  const input = ['a', 'b', 'a', 'c', 'b', 'a'];
+  const expectedOutput = { a: 3, b: 2, c: 1 };
+  const result = tally(input);
+  expect(result).toEqual(expectedOutput);
+});
 
 // Given an invalid input like a string
 // When passed to tally
 // Then it should throw an error
+test("tally on an invalid input throws an error", () => {
+  expect(() => tally("invalid")).toThrowError("Invalid input");
+});

Sprint-2/interpret/invert.js

@@ -6,6 +6,8 @@
 
 // E.g. invert({x : 10, y : 20}), target output: {"10": "x", "20": "y"}
 
+/*
+
 function invert(obj) {
   const invertedObj = {};
 
@@ -17,13 +19,40 @@ function invert(obj) {
 }
 
 // a) What is the current return value when invert is called with { a : 1 }
+console.log(invert({ a: 1 })); // returns { key: 1 }
 
 // b) What is the current return value when invert is called with { a: 1, b: 2 }
+console.log(invert({ a: 1, b: 2 })); // returns { key: 2 }
+
+*/
 
 // c) What is the target return value when invert is called with {a : 1, b: 2}
+// target output: {"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. It is needed in this program to easily iterate 
+// over the key-value pairs of the input 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
+// incorrectly assigns the value to the key in the inverted object. 
+// It uses `invertedObj.key = value` instead of `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;
+}
+
+// Tests
+console.log(invert({ a: 1 })); // returns { "1": "a" }
+console.log(invert({ a: 1, b: 2 })); // returns { "1": "a", "2": "b" }
+console.log(invert({ x: 10, y: 20 })); // returns { "10": "x", "20": "y" }

Sprint-2/stretch/count-words.js

@@ -26,3 +26,37 @@
 
 3. Order the results to find out which word is the most common in the input
 */
+
+function countWords(str) {
+  if (typeof str !== 'string') {
+    throw new Error("Invalid input: expected a string");
+  }
+
+  // Remove punctuation and normalize to lowercase
+  const cleanedText = str
+    .replace(/[.,!?]/g, '')  // Remove punctuation
+    .toLowerCase();          // Convert to lowercase
+
+  const words = cleanedText.split(/\s+/); // Split by whitespace
+  const counts = {};
+
+  for (const word of words) {
+    if (word === '') continue; // Skip empty strings
+    counts[word] = (counts[word] || 0) + 1;
+  }
+
+  // Sort by most common words
+  const sortedCounts = Object.fromEntries(
+    Object.entries(counts).sort(([, a], [, b]) => b - a)
+  );
+
+  return sortedCounts;
+}
+
+// Test cases:
+
+console.log(countWords("You and me, and YOU!")); 
+// Output: { you: 2, and: 2, me: 1 }
+
+console.log(countWords("Hello, world! Hello again.")); 
+// Output: { hello: 2, world: 1, again: 1 }