London | 25-ITP-SEP | Adnaan Abo | Sprint 2 | Coursework

Sprint-2/debug/address.js

@@ -1,4 +1,8 @@
 // Predict and explain first...
+/* address[0] does not access the houseNumber property of the address object. In JavaScript, objects are 
+accessed using their property names, not numerical indices. Therefore, address[0] is undefined because 
+there is no property with the key '0' in the address object. To access the houseNumber property, we should 
+use address.houseNumber or address['houseNumber']. */
 
 // 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...
+/* In JavaScript, objects are not iterable by default, which means you cannot use a for...of loop directly on an object. 
+The for...of loop is designed to work with iterable objects like arrays, strings, maps, and sets. Since the 'author' object 
+is not iterable, attempting to use for...of on it will result in a TypeError. To iterate over the properties of an object, 
+we can use Object.keys(), Object.values(), or Object.entries().*/
 
 // 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...
+/* In JavaScript, when you try to log an object directly within a template literal, it doesn't automatically
+format the object in a readable way. Instead, it converts the object to a string, which results in "[object Object]".
+To properly display the ingredients on new lines, we need to join the array elements into a single string with 
+newline characters in between.*/
 
 // This program should log out the title, how many it serves and the ingredients.
 // Each ingredient should be logged on a new line
@@ -11,5 +15,8 @@ const recipe = {
 };
 
 console.log(`${recipe.title} serves ${recipe.serves}
-  ingredients:
-${recipe}`);
+Ingredients:
+${recipe.ingredients.map(ingredient => `-${ingredient}`).join("\n")}`);
+// Using map to format each ingredient and join to create a single string with new lines 
+// between each ingredient.
+

Sprint-2/implement/contains.js

@@ -1,3 +1,16 @@
-function contains() {}
+// function that checks if a given property exists in an object
+function contains(obj, property) {
+  // Check if the input is a valid object and not null or an array
+  if (
+    typeof obj === "object" &&
+    obj !== null &&
+    !Array.isArray(obj) &&
+    Object.hasOwn(obj, property)
+  ) {
+    return true;
+  } else {
+    return false;
+  }
+}
 
 module.exports = contains;

Sprint-2/implement/contains.test.js

@@ -17,19 +17,32 @@ 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
 
-// Given an empty object
-// When passed to contains
+// When passed an empty object
 // Then it should return false
-test.todo("contains on empty object returns false");
+test("contains on empty object returns false", () => {
+  const emptyObject = {};
+  expect(contains(emptyObject, "key")).toBe(false);
+});
 
-// Given an object with properties
-// When passed to contains with an existing property name
-// Then it should return true
-
-// Given an object with properties
-// When passed to contains with a non-existent property name
+// When passed a non-object value (e.g., array, string, number, null, undefined)
 // Then it should return false
+test("Checks if an object contains the specified property", () => {
+  const obj1 = { name: "Alice", age: 30 };
+  expect(contains(obj1, "name")).toBe(true); // The property "name" exists
+  expect(contains(obj1, "city")).toBe(false); // The property "city" does not exist
+});
+
+// contains({ a: 1, b: 2 }, 'a') // returns true and contains({ a: 1, b: 2 }, 'c') // returns false
+test("Checks if an object contains the specified property", () => {
+  const obj1 = { a: 1, b: 2 };
+  expect(contains(obj1, "a")).toBe(true); // The property "name" exists
+  expect(contains(obj1, "c")).toBe(false); // The property "c" does not exist
+});
+
+
+// when given an array instead of an object returns false
+test(" when given an array instead of an object returns false", () => {
+  const arrayInput = ["value1", "value2"];
+  expect(contains(arrayInput, "key")).toBe(false); // The property "key" does not exist
+});
 
-// Given invalid parameters like an array
-// When passed to contains
-// Then it should return false or throw an error

Sprint-2/implement/lookup.js

@@ -1,5 +1,17 @@
-function createLookup() {
-  // implementation here
+function createLookup(pairs) {
+  /**
+   * Creates a lookup object from an array of [key, value] pairs.
+   * @param {Array<Array<string>>} pairs - An array of [countryCode, currencyCode] pairs.
+   * @returns {Object} - A lookup object mapping country codes to currency codes.
+   */
+  if (!Array.isArray(pairs)) {
+    throw new TypeError("Argument must be an array of pairs");
+  }
+
+  return pairs.reduce((lookup, [country, currency]) => {
+    lookup[country] = currency;
+    return lookup;
+  }, {});
 }
 
 module.exports = createLookup;

Sprint-2/implement/lookup.test.js

@@ -1,7 +1,19 @@
 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"],
+    ["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

Sprint-2/implement/querystring.js

@@ -1,13 +1,21 @@
 function parseQueryString(queryString) {
   const queryParams = {};
-  if (queryString.length === 0) {
+  if (!queryString || queryString.length === 0) {
     return queryParams;
   }
+
   const keyValuePairs = queryString.split("&");
 
   for (const pair of keyValuePairs) {
-    const [key, value] = pair.split("=");
-    queryParams[key] = value;
+    if (!pair) continue; // skip empty entries (e.g. trailing &)
+    const [key, ...rest] = pair.split("=");
+    const value = rest.length > 0 ? rest.join("=") : null;
+
+    // Decode URI components
+    const decodedKey = decodeURIComponent(key);
+    const decodedValue = value === null ? null : decodeURIComponent(value);
+
+    queryParams[decodedKey] = decodedValue;
   }
 
   return queryParams;

Sprint-2/implement/querystring.test.js

@@ -10,3 +10,51 @@ test("parses querystring values containing =", () => {
     "equation": "x=y+1",
   });
 });
+
+// Additional test cases to cover more edge cases
+// query strings with multiple key-value pairs
+test("parses querystring with multiple & and =", () => {
+  expect(parseQueryString("a=1&b=2&c=3")).toEqual({
+    "a": "1",
+    "b": "2",
+    "c": "3",
+  });
+});
+
+// query strings with empty keys
+test("parses querystring with empty value", () => {
+  expect(parseQueryString("key=")).toEqual({
+    "key": "",
+  });
+});
+
+// query strings with no value
+test("parses querystring with no value", () => {
+  expect(parseQueryString("flag")).toEqual({
+    "flag": null,
+  });
+});
+
+// query strings with encoded characters
+test("parses querystring with encoded characters", () => {
+  expect(parseQueryString("name=John%20Doe&city=New%20York")).toEqual({
+    "name": "John Doe",
+    "city": "New York",
+  });
+});
+
+// query strings with repeated keys
+test("parses querystring with repeated keys", () => {
+  expect(parseQueryString("key=1&key=2")).toEqual({
+    "key": "2", // assuming last value wins
+  });
+});
+
+// query strings with trailing &
+test("parses querystring with trailing &", () => {
+  expect(parseQueryString("key1=value1&key2=value2&")).toEqual({
+    "key1": "value1",
+    "key2": "value2",
+  });
+});
+

Sprint-2/implement/tally.js

@@ -1,3 +1,18 @@
-function tally() {}
+function tally(items) {
+  if (!Array.isArray(items)) {
+    throw new Error("Input must be an array");
+  }
 
+  const result = Object.create(null); // Create a clean object with no prototype
+
+  for (const item of items) {
+    if (result[item]) {
+      result[item]++;
+    } else {
+      result[item] = 1;
+    }
+  }
+
+  return result;
+}
 module.exports = tally;

Sprint-2/implement/tally.test.js

@@ -20,15 +20,29 @@ const tally = require("./tally.js");
 // When passed an array of items
 // Then it should return an object containing the count for each unique item
 
+test("tally counts unique items in an array", () => {
+  expect(tally(["a"])).toEqual({ a: 1 });
+  expect(tally(["a", "a", "a"])).toEqual({ a: 3 });
+  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 duplicate items
 // When passed to tally
 // Then it should return counts for each unique item
+test("tally counts duplicates correctly", () => {
+  expect(tally(["apple", "banana", "apple"])).toEqual({ apple: 2, banana: 1 });
+});
 
 // Given an invalid input like a string
 // When passed to tally
 // Then it should throw an error
+test("tally throws error for non-array input", () => {
+  expect(() => tally("not an array")).toThrow("Input must be an array");
+});

Sprint-2/interpret/invert.js

@@ -10,20 +10,34 @@ 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) Current return value: { key: 1 }
+// a) Target return value: { 1: "a" }
 
 // b) What is the current return value when invert is called with { a: 1, b: 2 }
+// b) Current return value: { key: 2 }
+// b) Target return value: { 1: "a", 2: "b" }
 
 // c) What is the target return value when invert is called with {a : 1, b: 2}
+// c) Current return value: { key: 2 }
+// c) Target return value: { 1: "a", 2: "b" }
 
 // c) What does Object.entries return? Why is it needed in this program?
+// c) Object.entries returns an array of a given object's own enumerable string-keyed property [key, value] pairs.
+// c) It is needed in this program to iterate over each key-value pair in the input object so that we can swap them and build the inverted object.
 
 // d) Explain why the current return value is different from the target output
+// d) The current return value is different from the target output because the implementation incorrectly assigns the value to a fixed key 'key' 
+// in the inverted object, rather than using the actual value from the original object as the key in the inverted object. This results in only the 
+// last processed value being stored under the same key 'key', overwriting any previous entries.
 
 // e) Fix the implementation of invert (and write tests to prove it's fixed!)
+// e) Fixed implementation is provided above. Below are the test cases in a separate file.
+
+module.exports = invert;

Sprint-2/interpret/inverts.test.js

@@ -0,0 +1,26 @@
+const invert = require("./invert");
+
+// Test cases for single key-value pair
+test("inverts a single key-value pair", () => {
+  expect(invert({ a: 1 })).toEqual({ 1: "a" });
+});
+
+// Test cases for multiple key-value pairs
+test("inverts multiple key-value pairs", () => {
+  expect(invert({ a: 1, b: 2 })).toEqual({ 1: "a", 2: "b" });
+});
+
+// Test cases for string values
+test("inverts string values", () => {
+  expect(invert({ a: "x", b: "y" })).toEqual({ x: "a", y: "b" });
+});
+
+// Test cases for mixed value types
+test("overwrites keys when values are not unique", () => {
+  expect(invert({ a: 1, b: 1 })).toEqual({ 1: "b" }); // last one wins
+});
+
+// Test cases for empty object
+test("inverts an empty object", () => {
+  expect(invert({})).toEqual({});
+});