London | 26-ITP-January | Eugenie Ahangama | Sprint 2 | Data Groups

Sprint-2/debug/address.js

@@ -1,4 +1,8 @@
 // Predict and explain first...
+// address is an object, not an array
+// address[0] looks for a property named "0",
+// which doesn't exist → returns undefined
+// So the log will say: My house number is undefined
 
 // This code should log out the houseNumber from the address object
 // but it isn't working...
@@ -12,4 +16,4 @@ 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

@@ -1,4 +1,8 @@
 // Predict and explain first...
+// The 'author' variable is an object, not an array or string.
+// for..of loops require an iterable, but plain objects are not iterable.
+// This will throw a TypeError: author is not iterable.
+// Nothing will be logged to the console.
 
 // 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 +15,6 @@ const author = {
   alive: true,
 };
 
-for (const value of author) {
+for (const value of Object.values(author)) {
   console.log(value);
 }

Sprint-2/debug/recipe.js

@@ -1,4 +1,8 @@
 // Predict and explain first...
+// The template literal ${recipe} attempts to convert the entire object to a string.
+// Because objects aren't strings, it will log: "[object Object]".
+// It also fails to access the specific 'ingredients' array or loop through them.
+// The result will be one confusing line instead of a formatted list.
 
 // This program should log out the title, how many it serves and the ingredients.
 // Each ingredient should be logged on a new line
@@ -10,6 +14,9 @@ const recipe = {
   ingredients: ["olive oil", "tomatoes", "salt", "pepper"],
 };
 
-console.log(`${recipe.title} serves ${recipe.serves}
-  ingredients:
-${recipe}`);
+console.log(`${recipe.title} serves ${recipe.serves}`);
+console.log(" ingredients:");
+
+for (const ing of recipe.ingredients) {
+  console.log(` - ${ing}`);
+}

Sprint-2/implement/contains.js

@@ -1,3 +1,12 @@
-function contains() {}
+function contains(object, propertyName) {
+  // return false if object is null/defined or not an object
+  if (object == null) return false;
+  // typeof check + reject arrays
+  if (typeof object !== "object") return false;
+  if (Array.isArray(object)) return false;
+
+  // Use Object.hasOwn to check only own properties
+  return Object.hasOwn(object, propertyName);
+}
 
 module.exports = contains;

Sprint-2/implement/contains.test.js

@@ -16,20 +16,40 @@ 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 when the property exists in the object", () => {
+  expect(contains({ a: 1, b: 2 }, "a")).toBe(true);
+  expect(contains({ a: 1, b: 2 }, "b")).toBe(true);
+});
 
 // 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);
+  expect(contains({}, "toString")).toBe(false);
+});
 
 // Given an object with properties
 // When passed to contains with an existing property name
 // Then it should return true
+test("returns true for existing property name", () => {
+  expect(contains({ name: "Alex" }, "name")).toBe(true);
+  expect(contains({ id: 42 }, "id")).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 for non-existent property name", () => {
+  expect(contains({ name: "Alex", age: 42 }, "email")).toBe(false);
+  expect(contains({ age: 54 }, "name")).toBe(false);
+});
 
 // Given invalid parameters like an array
 // When passed to contains
 // Then it should return false or throw an error
+test("handles invalid parameters like an array", () => {
+  expect(contains([], "length")).toBe(false);
+  expect(contains(123, "length")).toBe(false);
+  expect(contains("string", "length")).toBe(false);
+});

Sprint-2/implement/lookup.js

@@ -1,5 +1,16 @@
-function createLookup() {
+function createLookup(pairs) {
   // implementation here
+  // Creates empty object that will store our,
+  // country → currency
+  const lookup = {};
+  // Loop through each pair in the input array
+  for (const [country, currency] of pairs) {
+    // Use the country code as they key
+    // Assigns the correspoding currency code as the value
+    lookup[country] = currency;
+  }
+  // returns the completed lookup object
+  return lookup;
 }
 
 module.exports = createLookup;

Sprint-2/implement/lookup.test.js

@@ -1,6 +1,17 @@
 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 pairs = [
+    ["US", "USD"],
+    ["CA", "CAD"],
+  ];
+  const result = createLookup(pairs);
+
+  expect(result).toEqual({
+    US: "USD",
+    CA: "CAD",
+  });
+});
 
 /*
 

Sprint-2/implement/querystring.js

@@ -1,13 +1,30 @@
 function parseQueryString(queryString) {
   const queryParams = {};
-  if (queryString.length === 0) {
+
+  // Handle empty string or just "?"
+  if (!queryString || queryString === "?") {
     return queryParams;
   }
-  const keyValuePairs = queryString.split("&");
 
-  for (const pair of keyValuePairs) {
-    const [key, value] = pair.split("=");
-    queryParams[key] = value;
+  // Remove leading ? if present
+  const cleaned = queryString.startsWith("?")
+    ? queryString.slice(1)
+    : queryString;
+
+  // Split into segments and ignore empty ones
+  const segments = cleaned.split("&").filter(Boolean);
+
+  for (const segment of segments) {
+    // Split only on the first =, but everything after is a value
+    const eqIndex = segment.indexOf("=");
+
+    const key = eqIndex === -1 ? segment : segment.slice(0, eqIndex);
+    const value = eqIndex === -1 ? "" : segment.slice(eqIndex + 1);
+
+    if (key) {
+      // Decode percent-encoded characters in both key and value
+      queryParams[decodeURIComponent(key)] = decodeURIComponent(value);
+    }
   }
 
   return queryParams;

Sprint-2/implement/querystring.test.js

@@ -3,10 +3,58 @@
 // 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("handles multiple parameters", () => {
+  expect(parseQueryString("name=Alex&age=25&city=London")).toEqual({
+    name: "Alex",
+    age: "25",
+    city: "London",
+  });
+});
+
+test("handles empty value (key=)", () => {
+  expect(parseQueryString("search=&page=3")).toEqual({
+    search: "",
+    page: "3",
+  });
+});
+
+test("handles key without value", () => {
+  expect(parseQueryString("debug&sort=asc")).toEqual({
+    debug: "",
+    sort: "asc",
+  });
+});
+
+test("handles leading question mark", () => {
+  expect(parseQueryString("?q=javascript&lang=en")).toEqual({
+    q: "javascript",
+    lang: "en",
+  });
+});
+
+test("returns empty object when input is empty or just ?", () => {
+  expect(parseQueryString("")).toEqual({});
+  expect(parseQueryString("?")).toEqual({});
+});
+
+test("ignores trailing &", () => {
+  expect(parseQueryString("a=1&b=2&")).toEqual({
+    a: "1",
+    b: "2",
+  });
+});
+
+test("ignores repeated &", () => {
+  expect(parseQueryString("x=10&&y=20")).toEqual({
+    x: "10",
+    y: "20",
   });
 });

Sprint-2/implement/tally.js

@@ -1,3 +1,23 @@
-function tally() {}
+function tally(arr) {
+  // Check if the input is not an array
+  if (!Array.isArray(arr)) {
+    // If it's not an array, stop the function
+    // and throw an error message
+    throw new Error("Input must be an array");
+  }
+
+  // Create an empty object with no inherited properties
+  // This prevents conflicts with built in properties like "toString"
+  const counts = Object.create(null);
+
+  // Loop through each item in the array one by one
+  for (const item of arr) {
+    // If the item already exists in counts, add 1 to it
+    // If it doesn't exist yet (undefined), start it at 0 then add 1
+    counts[item] = (counts[item] || 0) + 1;
+  }
+  // Return the finished counts object once all items have been tallied
+  return counts;
+}
 
 module.exports = tally;

Sprint-2/implement/tally.test.js

@@ -19,16 +19,42 @@ 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 returns an object containing the count for each unique item", () => {
+  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 a single item
+// When passed to tally
+// Then it should return a count of 1 for that item
+test("tally on an array with one item returns count of 1", () => {
+  expect(tally(["a"])).toEqual({
+    a: 1,
+  });
+});
 
 // 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(["a", "a", "a"])).toEqual({
+    a: 3,
+  });
+});
 
 // Given an invalid input like a string
 // When passed to tally
 // Then it should throw an error
+test("tally throws an error for invalid input", () => {
+  expect(() => tally("abc")).toThrow("Input must be an array");
+});

Sprint-2/interpret/invert.js

@@ -7,23 +7,42 @@
 // E.g. invert({x : 10, y : 20}), target output: {"10": "x", "20": "y"}
 
 function invert(obj) {
+  // Check if the input is not an object
+  if (typeof obj !== "object" || obj === null || Array.isArray(obj)) {
+    throw new Error("Input must be an object");
+  }
+
   const invertedObj = {};
 
+  // Loop through each key value pair and swap them
   for (const [key, value] of Object.entries(obj)) {
-    invertedObj.key = value;
+    // bracket notation uses the variable,
+    // not the literal string "key"
+    invertedObj[value] = key;
   }
 
   return invertedObj;
 }
 
+module.exports = invert;
+
 // a) What is the current return value when invert is called with { a : 1 }
+// The current return value when invert is called with { a : 1 } is { key:1 }
 
 // b) What is the current return value when invert is called with { a: 1, b: 2 }
+// The current return value when invert is called with { a: 1, b: 2 } is { key:2 }
 
 // c) What is the target return value when invert is called with {a : 1, b: 2}
+// The target return value when invert is called with {a : 1, b: 2} is { "1": "a", "2": "b" }
 
 // c) What does Object.entries return? Why is it needed in this program?
+// Object.entries converts an object into an array of [key, value] pairs,
+// it's needed so you can loop through both the key and value at the same time
 
 // d) Explain why the current return value is different from the target output
+// The bug is invertedObj.key = value - dot notation sets a literal key called "key",
+// instead of using the variable. It also overwrites itseld on every loop iteration,
+// so you only ever get the last value.
 
 // e) Fix the implementation of invert (and write tests to prove it's fixed!)
+// Fixed implementation of invert and added tests cases to prove it's fixed.

Sprint-2/interpret/invert.test.js

@@ -0,0 +1,38 @@
+const invert = require("./invert.js");
+
+// Given an object
+// When invert is passed this object
+// Then it should swap the keys and values
+test("invert swaps the keys and values of an object", () => {
+  expect(invert({ x: 10, y: 20 })).toEqual({
+    10: "x",
+    20: "y",
+  });
+});
+
+// Given an object with one key value pair
+// When passed to invert
+// Then it should return the swapped pair
+test("invert swaps a single key value pair", () => {
+  expect(invert({ a: 1 })).toEqual({
+    1: "a",
+  });
+});
+
+// Given an empty object
+// When passed to invert
+// Then it should return an empty object
+test("invert on an empty object returns an empty object", () => {
+  expect(invert({})).toEqual({});
+});
+
+// Given an invalid input like an array, string, number, null or undefined
+// When passed to invert
+// Then it should throw an error
+test("invert throws an error for invalid input", () => {
+  expect(() => invert([])).toThrow("Input must be an object");
+  expect(() => invert("hello")).toThrow("Input must be an object");
+  expect(() => invert(123)).toThrow("Input must be an object");
+  expect(() => invert(null)).toThrow("Input must be an object");
+  expect(() => invert(undefined)).toThrow("Input must be an object");
+});