Birmingham | 26-ITP-May | Gabriel Pawuoi | Sprint 2 |debug address/author/recipe, implement contains/lookup/tall

Sprint-2/debug/address.js

@@ -4,6 +4,14 @@
 // but it isn't working...
 // Fix anything that isn't working
 
+// PREDICTION: The code will log "My house number is undefined" because address[0]
+// tries to access the element at index 0 like an array, but address is an object.
+// Objects don't have numeric indexes — they have named keys like "houseNumber".
+
+// EXPLANATION: address[0] looks for a key literally named "0" on the object,
+// which doesn't exist, so it returns undefined.
+// The fix is to use address.houseNumber (dot notation) or address["houseNumber"] (bracket notation).
+
 const address = {
   houseNumber: 42,
   street: "Imaginary Road",
@@ -12,4 +20,4 @@ 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

@@ -3,6 +3,13 @@
 // 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
 
+// PREDICTION: The code will throw a TypeError: author is not iterable.
+
+// EXPLANATION: for...of works on iterables (arrays, strings, Maps, Sets etc.).
+// Plain objects are NOT iterable by default, so you cannot use for...of directly
+// on an object. To iterate over an object's values, you need Object.values(author)
+// which returns an array of the values that for...of can then loop over.
+
 const author = {
   firstName: "Zadie",
   lastName: "Smith",
@@ -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

@@ -4,6 +4,14 @@
 // Each ingredient should be logged on a new line
 // How can you fix it?
 
+// PREDICTION: The code will log "bruschetta serves 2" then "ingredients:"
+// then "[object Object]" — because embedding an object directly in a template
+// literal calls .toString() on it, which returns "[object Object]".
+
+// EXPLANATION: recipe is an object, so ${recipe} just gives "[object Object]".
+// We need to access the ingredients array specifically and join its items
+// with newlines: ${recipe.ingredients.join("\n")} logs each ingredient on its own line.
+
 const recipe = {
   title: "bruschetta",
   serves: 2,
@@ -12,4 +20,4 @@ const recipe = {
 
 console.log(`${recipe.title} serves ${recipe.serves}
   ingredients:
-${recipe}`);
+${recipe.ingredients.join("\n")}`);

Sprint-2/implement/contains.js

@@ -1,3 +1,6 @@
-function contains() {}
+function contains(obj, prop) {
+  if (typeof obj !== "object" || obj === null || Array.isArray(obj)) return false;
+  return Object.prototype.hasOwnProperty.call(obj, prop);
+}
 
 module.exports = contains;

Sprint-2/implement/contains.test.js

@@ -1,35 +1,17 @@
 const contains = require("./contains.js");
 
-/*
-Implement a function called contains that checks an object contains a
-particular property
+test("contains on empty object returns false", () => {
+  expect(contains({}, "a")).toBe(false);
+});
 
-E.g. contains({a: 1, b: 2}, 'a') // returns true
-as the object contains a key of 'a'
+test("returns true when object has the property", () => {
+  expect(contains({ a: 1, b: 2 }, "a")).toBe(true);
+});
 
-E.g. contains({a: 1, b: 2}, 'c') // returns false
-as the object doesn't contains a key of 'c'
-*/
+test("returns false when object does not have the property", () => {
+  expect(contains({ a: 1, b: 2 }, "c")).toBe(false);
+});
 
-// 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");
-
-// 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
-// Then it should return 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 input", () => {
+  expect(contains([1, 2, 3], "0")).toBe(false);
+});

Sprint-2/implement/lookup.js

@@ -1,5 +1,5 @@
-function createLookup() {
-  // implementation here
+function createLookup(pairs) {
+  return Object.fromEntries(pairs);
 }
 
 module.exports = createLookup;

Sprint-2/implement/lookup.test.js

@@ -1,35 +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", () => {
+  expect(createLookup([["US", "USD"], ["CA", "CAD"]])).toEqual({ US: "USD", CA: "CAD" });
+});
 
-/*
+test("returns empty object for empty array", () => {
+  expect(createLookup([])).toEqual({});
+});
 
-Create a lookup object of key value pairs from an array of code pairs
-
-Acceptance Criteria:
-
-Given
- - An array of arrays representing country code and currency code pairs
-   e.g. [['US', 'USD'], ['CA', 'CAD']]
-
-When
- - createLookup function is called with the country-currency array as an argument
-
-Then
- - It should return an object where:
- - The keys are the country codes
- - The values are the corresponding currency codes
-
-Example
-Given: [['US', 'USD'], ['CA', 'CAD']]
-
-When
-createLookup(countryCurrencyPairs) is called
-
-Then
-It should return:
- {
-   'US': 'USD',
-   'CA': 'CAD'
- }
-*/
+test("creates lookup for a single pair", () => {
+  expect(createLookup([["GB", "GBP"]])).toEqual({ GB: "GBP" });
+});

Sprint-2/implement/querystring.js

@@ -1,13 +1,26 @@
 function parseQueryString(queryString) {
   const queryParams = {};
-  if (queryString.length === 0) {
-    return queryParams;
-  }
-  const keyValuePairs = queryString.split("&");
+  if (queryString.length === 0) return queryParams;
+
+  const keyValuePairs = queryString.split("&").filter(pair => pair.length > 0);
 
   for (const pair of keyValuePairs) {
-    const [key, value] = pair.split("=");
-    queryParams[key] = value;
+    const eqIndex = pair.indexOf("=");
+    const rawKey = eqIndex === -1 ? pair : pair.slice(0, eqIndex);
+    const rawValue = eqIndex === -1 ? "" : pair.slice(eqIndex + 1);
+
+    const key = decodeURIComponent(rawKey.replace(/\+/g, " "));
+    const value = decodeURIComponent(rawValue.replace(/\+/g, " "));
+
+    if (Object.prototype.hasOwnProperty.call(queryParams, key)) {
+      if (Array.isArray(queryParams[key])) {
+        queryParams[key].push(value);
+      } else {
+        queryParams[key] = [queryParams[key], value];
+      }
+    } else {
+      queryParams[key] = value;
+    }
   }
 
   return queryParams;

Sprint-2/implement/tally.js

@@ -1,3 +1,9 @@
-function tally() {}
+function tally(arr) {
+  if (!Array.isArray(arr)) throw new Error("Input must be an array");
+  return arr.reduce((acc, item) => {
+    acc[item] = (acc[item] || 0) + 1;
+    return acc;
+  }, {});
+}
 
 module.exports = tally;

Sprint-2/implement/tally.test.js

@@ -1,34 +1,21 @@
 const tally = require("./tally.js");
 
-/**
- * tally array
- *
- * In this task, you'll need to implement a function called tally
- * that will take a list of items and count the frequency of each item
- * in an array
- *
- * For example:
- *
- * tally(['a']), target output: { a: 1 }
- * tally(['a', 'a', 'a']), target output: { a: 3 }
- * tally(['a', 'a', 'b', 'c']), target output: { a : 2, b: 1, c: 1 }
- */
+test("tally on an empty array returns an empty object", () => {
+  expect(tally([])).toEqual({});
+});
 
-// Acceptance criteria:
+test("tally counts a single item", () => {
+  expect(tally(["a"])).toEqual({ a: 1 });
+});
 
-// 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 counts duplicate items", () => {
+  expect(tally(["a", "a", "a"])).toEqual({ a: 3 });
+});
 
-// 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 counts multiple unique items", () => {
+  expect(tally(["a", "a", "b", "c"])).toEqual({ a: 2, b: 1, c: 1 });
+});
 
-// Given an array with duplicate items
-// When passed to tally
-// Then it should return counts for each unique item
-
-// Given an invalid input like a string
-// When passed to tally
-// Then it should throw an error
+test("throws an error for invalid input like a string", () => {
+  expect(() => tally("invalid")).toThrow();
+});

Sprint-2/interpret/invert.js

@@ -10,20 +10,46 @@ 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 }
+// ANSWER: The ORIGINAL (broken) code had invertedObj.key = value, which always sets
+// a literal property named "key" rather than using the variable. So calling
+// invert({ a: 1 }) would return { key: 1 } — the key name is the string "key",
+// not "1" as intended.
 
 // b) What is the current return value when invert is called with { a: 1, b: 2 }
+// ANSWER: With the original broken code, each iteration overwrites the same "key"
+// property, so the result would be { key: 2 } — only the last value survives
+// because every iteration does invertedObj.key = value (literal property "key").
 
 // c) What is the target return value when invert is called with {a : 1, b: 2}
+// ANSWER: { "1": "a", "2": "b" }
+// The keys and values are swapped: original keys become values, original values
+// become keys. Object keys are always strings, so the numbers 1 and 2 become "1" and "2".
 
 // c) What does Object.entries return? Why is it needed in this program?
+// ANSWER: Object.entries(obj) returns an array of [key, value] pairs for every
+// property in the object. For example, Object.entries({ a: 1, b: 2 }) returns
+// [["a", 1], ["b", 2]]. It is needed here because for...of cannot loop over a
+// plain object directly \u2014 it only works on iterables like arrays. Object.entries
+// converts the object into an iterable array of pairs so we can destructure each
+// [key, value] and swap them.
 
 // d) Explain why the current return value is different from the target output
+// ANSWER: The original code used invertedObj.key = value (dot notation with the
+// literal word "key") instead of invertedObj[value] = key (bracket notation using
+// the variable). Dot notation always creates a property with the exact name you
+// type \u2014 "key" \u2014 rather than using the variable's value as the property name.
+// Bracket notation evaluates the expression inside the brackets, so invertedObj[value]
+// correctly uses whatever value holds (e.g. 1, 2) as the new key name.
 
 // e) Fix the implementation of invert (and write tests to prove it's fixed!)
+// ANSWER: Fixed above \u2014 changed invertedObj.key = value  to  invertedObj[value] = key
+// Tests are in a separate invert.test.js file.
+
+module.exports = invert;