London | ITP-MAY-25 | Surafel Workneh| Module: Data Groups | Sprint-2

Sprint-2/debug/address.js

@@ -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"]}`);//address is an object, not an array

Sprint-2/debug/author.js

@@ -11,6 +11,6 @@ const author = {
   alive: true,
 };
 
-for (const value of author) {
+for (const value of Object.values(author)) {//accessing both key and value using se Object.values()
   console.log(value);
 }

Sprint-2/debug/recipe.js

@@ -12,4 +12,4 @@ const recipe = {
 
 console.log(`${recipe.title} serves ${recipe.serves}
   ingredients:
-${recipe}`);
+${recipe.ingredients.join("\n")}`); // ingredients in new array

Sprint-2/implement/contains.js

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

Sprint-2/implement/contains.test.js

@@ -1,35 +1,37 @@
 const contains = require("./contains.js");
 
-/*
-Implement a function called contains that checks an object contains a
-particular property
-
-E.g. contains({a: 1, b: 2}, 'a') // returns true
-as the object contains a key of 'a'
-
-E.g. contains({a: 1, b: 2}, 'c') // returns false
-as the object doesn't contains a key of 'c'
-*/
-
-// Acceptance criteria:
-
-// 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
-
 // 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({}, "key")).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", () => {
+  expect(contains({ name: "Alice", age: 30 }, "name")).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", () => {
+  expect(contains({ name: "Alice", age: 30 }, "email")).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 array instead of object", () => {
+  expect(contains(["a", "b", "c"], "a")).toBe(false);
+});
+
+test("returns false for null input", () => {
+  expect(contains(null, "key")).toBe(false);
+});
+
+test("returns false for undefined input", () => {
+  expect(contains(undefined, "key")).toBe(false);
+});

Sprint-2/implement/lookup.js

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

Sprint-2/implement/lookup.test.js

@@ -1,7 +1,15 @@
 const createLookup = require("./lookup.js");
 
-test.todo("creates a country currency code lookup for multiple codes");
-
+//  Core Test: Normal input of multiple country-currency pairs
+test("creates a country currency code lookup for multiple codes", () => {
+  const input = [['US', 'USD'], ['CA', 'CAD'], ['JP', 'JPY']];
+  const expected = {
+    US: 'USD',
+    CA: 'CAD',
+    JP: 'JPY',
+  };
+  expect(createLookup(input)).toEqual(expected);
+});
 /*
 
 Create a lookup object of key value pairs from an array of code pairs
@@ -33,3 +41,13 @@ It should return:
    'CA': 'CAD'
  }
 */
+// Edge Case 1: Empty array input
+test("returns empty object when given an empty array", () => {
+  expect(createLookup([])).toEqual({});
+});
+// dge Case 2: Duplicate country codes (last value wins)
+test("overwrites value if country code is duplicated", () => {
+  const input = [['US', 'USD'], ['US', 'US Dollars']];
+  const expected = { US: 'US Dollars' };
+  expect(createLookup(input)).toEqual(expected);
+});

Sprint-2/implement/querystring.js

@@ -1,13 +1,20 @@
 function parseQueryString(queryString) {
   const queryParams = {};
-  if (queryString.length === 0) {
-    return queryParams;
-  }
+  if (!queryString) return queryParams;
+
   const keyValuePairs = queryString.split("&");
 
   for (const pair of keyValuePairs) {
-    const [key, value] = pair.split("=");
-    queryParams[key] = value;
+    const indexOfEqual = pair.indexOf("=");
+
+    if (indexOfEqual === -1) {
+      // No '=' means key with no value
+      queryParams[decodeURIComponent(pair)] = "";
+    } else {
+      const key = decodeURIComponent(pair.slice(0, indexOfEqual));
+      const value = decodeURIComponent(pair.slice(indexOfEqual + 1));
+      queryParams[key] = value;
+    }
   }
 
   return queryParams;

Sprint-2/implement/querystring.test.js

@@ -10,3 +10,35 @@ test("parses querystring values containing =", () => {
     "equation": "x=y+1",
   });
 });
+
+//Test: Handles URL-encoded characters (e.g. space encoded as %20)
+test("decodes percent-encoded characters", () => {
+  expect(parseQueryString("note=hello%20world")).toEqual({
+    note: "hello world",
+  });
+});
+
+// Test: Key without a value (e.g. justKey)
+// Should treat missing value as an empty string
+
+test("parses key without value", () => {
+  expect(parseQueryString("justKey")).toEqual({
+    justKey: "",
+  });
+});
+
+// Test: Empty query string
+
+test("returns empty object for empty query string", () => {
+  expect(parseQueryString("")).toEqual({});
+});
+
+
+// Test: Handles multiple pairs including one with no value
+
+test("handles mixed keys with and without values", () => {
+  expect(parseQueryString("name=Alice&flag")).toEqual({
+    name: "Alice",
+    flag: "",
+  });
+});

Sprint-2/implement/tally.js

@@ -1,3 +1,15 @@
-function tally() {}
+function tally(arr) {
+  if (!Array.isArray(arr)) {
+    throw new Error("Input must be an array");
+  }
+
+  const counts = {};
+
+  for (const item of arr) {
+    counts[item] = (counts[item] || 0) + 1;
+  }
+
+  return counts;
+}
 
 module.exports = tally;

Sprint-2/implement/tally.test.js

@@ -23,12 +23,19 @@ 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({});
+});
 
 // Given an array with duplicate items
 // When passed to tally
 // Then it should return counts for each unique item
-
+test("tally single item array", () => {
+  expect(tally(["a"])).toEqual({ a: 1 });
+});
 // Given an invalid input like a string
 // When passed to tally
 // Then it should throw an error
+test("tally throws error on invalid input (non-array)", () => {
+  expect(() => tally("not-an-array")).toThrow("Input must be an array");
+});

Sprint-2/interpret/invert.js

@@ -6,24 +6,48 @@
 
 // E.g. invert({x : 10, y : 20}), target output: {"10": "x", "20": "y"}
 
-function invert(obj) {
-  const invertedObj = {};
+// function invert(obj) {
+//   const invertedObj = {};
 
-  for (const [key, value] of Object.entries(obj)) {
-    invertedObj.key = value;
-  }
+//   for (const [key, value] of Object.entries(obj)) {
+//     invertedObj.key = value;
+//   }
 
-  return invertedObj;
-}
+//   return invertedObj;
+// }
 
 // a) What is the current return value when invert is called with { a : 1 }
+//{ key: 1 } // because  literally sets the property "key" instead of using the variable value as the new key.
 
 // b) What is the current return value when invert is called with { a: 1, b: 2 }
+//{ key: 2 } //because The second iteration of the loop overwrites the first one because it keeps writing to "key".
 
 // c) What is the target return value when invert is called with {a : 1, b: 2}
-
+//{ "1": "a", "2": "b" } // because Each key and value from the input object should be swapped.
+// Object.entries(obj) returns an array of [key, value] pairs from the object.
 // c) What does Object.entries return? Why is it needed in this program?
+// Object.entries({ a: 1, b: 2 }) 
+// → [['a', 1], ['b', 2]] because 
 
 // d) Explain why the current return value is different from the target output
-
+// The original code used invertedObj.key = value, which:
+// Created a property literally named "key"
+// Overwrote it in every loop
 // e) Fix the implementation of invert (and write tests to prove it's fixed!)
+function invert(obj) {
+  // Validate that input is a non-null object and not an array
+  if (typeof obj !== 'object' || obj === null || Array.isArray(obj)) {
+    throw new Error("Input must be a non-null object");
+  }
+
+  const invertedObj = {};
+
+  // Loop over key-value pairs using Object.entries
+  for (const [key, value] of Object.entries(obj)) {
+    // Swap the key and value
+    invertedObj[String(value)] = key;
+  }
+
+  return invertedObj;
+}
+module.exports = invert;

Sprint-2/interpret/invert.test.js

@@ -0,0 +1,24 @@
+const invert = require("./invert.js");
+
+// Test: empty object returns empty object
+test("returns empty object when given an empty object", () => {
+  expect(invert({})).toEqual({});
+});
+// Test: single key-value pair
+test("inverts a single key-value pair", () => {
+  expect(invert({ a: 1 })).toEqual({ 1: "a" });
+});
+
+// Test: multiple key-value pairs
+test("inverts multiple key-value pairs", () => {
+  expect(invert({ a: 1, b: 2 })).toEqual({ 1: "a", 2: "b" });
+});
+
+// Test: duplicate values (last one wins)
+test("overwrites key if values are not unique", () => {
+  expect(invert({ a: 1, b: 1 })).toEqual({ 1: "b" }); // 'b' overwrites 'a'
+});
+
+test("throws error if input is not an object", () => {
+  expect(() => invert("string")).toThrow("Input must be a non-null object");
+});