Sheffield | 26-ITP-Jan | Mahmoud Shaabo | Sprint 2 | Module-Data-Groups

Sprint-2/debug/address.js

@@ -1,9 +1,8 @@
 // Predict and explain first...
 
 // This code should log out the houseNumber from the address object
-// but it isn't working...
-// Fix anything that isn't working
 
+// Create an object that holds address details
 const address = {
   houseNumber: 42,
   street: "Imaginary Road",
@@ -12,4 +11,5 @@ const address = {
   postcode: "XYZ 123",
 };
 
-console.log(`My house number is ${address[0]}`);
+// Access the houseNumber property using dot notation
+console.log(`My house number is ${address.houseNumber}`);

Sprint-2/debug/author.js

@@ -1,8 +1,8 @@
 // Predict and explain first...
 
 // 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
 
+// Create an object that holds author details
 const author = {
   firstName: "Zadie",
   lastName: "Smith",
@@ -11,6 +11,24 @@ const author = {
   alive: true,
 };
 
-for (const value of author) {
+// Use Object.values() to get an array of all values, then loop over them
+for (const value of Object.values(author)) {
   console.log(value);
 }
+
+/*
+## Explanation of the Fix
+
+- Object.values(author) is a built-in function that takes an object and returns an array containing only the values. In our case it returns: ["Zadie", "Smith", "writer", 40, true]
+- Since the result is now an array, for...of works correctly and goes through each value one by one.
+
+## How to Test in the Terminal
+node author.js
+
+Expected output:
+Zadie
+Smith
+writer
+40
+true
+*/

Sprint-2/debug/recipe.js

@@ -2,14 +2,36 @@
 
 // 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?
 
+// Create an object that holds recipe details
 const recipe = {
   title: "bruschetta",
   serves: 2,
   ingredients: ["olive oil", "tomatoes", "salt", "pepper"],
 };
 
-console.log(`${recipe.title} serves ${recipe.serves}
-  ingredients:
-${recipe}`);
+// Log the title and how many it serves
+console.log(`${recipe.title} serves ${recipe.serves}`);
+
+// Log each ingredient on a new line using a loop
+for (const ingredient of recipe.ingredients) {
+  console.log(ingredient);
+}
+
+/*
+## Brief Explanation
+
+- recipe.ingredients is an array (a numbered list) containing four items.
+- for...of works on arrays, so it goes through each item one by one.
+- Each time through the loop, the variable ingredient holds the current item, and console.log prints it on its own line.
+
+## How to Test
+node recipe.js
+
+Expected output:
+bruschetta serves 2
+olive oil
+tomatoes
+salt
+pepper
+*/

Sprint-2/implement/contains.js

@@ -1,3 +1,12 @@
-function contains() {}
+// Check if an object contains a specific property
+function contains(object, propertyName) {
+  // If the input is not a valid object or is an array, return false
+  if (typeof object !== "object" || object === null || Array.isArray(object)) {
+    return false;
+  }
+
+  // Use hasOwnProperty to check if the key exists in the object
+  return object.hasOwnProperty(propertyName);
+}
 
 module.exports = contains;

Sprint-2/implement/contains.test.js

@@ -20,16 +20,27 @@ as the object doesn't contains a key of 'c'
 // 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 returns true for an existing property", () => {
+  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 returns false for a non-existent property", () => {
+  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 returns false when passed an array instead of an object", () => {
+  expect(contains(["a", "b"], "0")).toBe(false);
+});

Sprint-2/implement/lookup.js

@@ -1,5 +1,16 @@
-function createLookup() {
-  // implementation here
+// Take an array of pairs and return a lookup object
+function createLookup(pairs) {
+  // Create an empty object to store the results
+  const lookup = {};
+
+  // Loop through each pair in the array
+  for (const pair of pairs) {
+    // pair[0] is the key (country code), pair[1] is the value (currency code)
+    lookup[pair[0]] = pair[1];
+  }
+
+  // Return the completed lookup object
+  return lookup;
 }
 
 module.exports = createLookup;

Sprint-2/implement/lookup.test.js

@@ -1,7 +1,5 @@
 const createLookup = require("./lookup.js");
 
-test.todo("creates a country currency code lookup for multiple codes");
-
 /*
 
 Create a lookup object of key value pairs from an array of code pairs
@@ -33,3 +31,29 @@ It should return:
    'CA': 'CAD'
  }
 */
+
+// Given multiple country-currency pairs
+// When createLookup is called
+// Then it should return an object with country codes as keys and currency codes as values
+test("creates a country currency code lookup for multiple codes", () => {
+  const pairs = [
+    ["US", "USD"],
+    ["CA", "CAD"],
+    ["GB", "GBP"],
+  ];
+  expect(createLookup(pairs)).toEqual({ US: "USD", CA: "CAD", GB: "GBP" });
+});
+
+// Given a single country-currency pair
+// When createLookup is called
+// Then it should return an object with that one key-value pair
+test("creates a lookup for a single country-currency pair", () => {
+  expect(createLookup([["EG", "EGP"]])).toEqual({ EG: "EGP" });
+});
+
+// Given an empty array
+// When createLookup is called
+// Then it should return an empty object
+test("returns an empty object for an empty array", () => {
+  expect(createLookup([])).toEqual({});
+});

Sprint-2/implement/querystring.js

@@ -1,13 +1,35 @@
+// Parse a query string into an object of key-value pairs
 function parseQueryString(queryString) {
+  // Create an empty object to store the results
   const queryParams = {};
+
+  // If the input is empty, return the empty object
   if (queryString.length === 0) {
     return queryParams;
   }
+
+  // Split the string by "&" to get each key=value pair
   const keyValuePairs = queryString.split("&");
 
   for (const pair of keyValuePairs) {
-    const [key, value] = pair.split("=");
-    queryParams[key] = value;
+    // Skip empty pairs caused by double ampersands like "key1=value1&&key2=value2"
+    if (pair === "") {
+      continue;
+    }
+
+    // Find the position of the FIRST "=" only
+    const firstEqualIndex = pair.indexOf("=");
+
+    // If there is no "=", the whole pair is the key with an empty value
+    if (firstEqualIndex === -1) {
+      queryParams[pair] = "";
+    } else {
+      // Everything before the first "=" is the key
+      const key = pair.slice(0, firstEqualIndex);
+      // Everything after the first "=" is the value (may contain more "=" signs)
+      const value = pair.slice(firstEqualIndex + 1);
+      queryParams[key] = value;
+    }
   }
 
   return queryParams;

Sprint-2/implement/tally.js

@@ -1,3 +1,22 @@
-function tally() {}
+// Count the frequency of each item in an array
+function tally(items) {
+  // If the input is not an array, throw an error
+  if (!Array.isArray(items)) {
+    throw new Error("Input must be an array");
+  }
+
+  // Create an empty object to store the counts
+  const counts = Object.create(null);
+
+  // Loop through each item in the array
+  for (const item of items) {
+    // If this item already exists in counts, add 1 to it
+    // If it does not exist yet, start at 1
+    counts[item] = (counts[item] || 0) + 1;
+  }
+
+  // Return the object with all the counts
+  return counts;
+}
 
 module.exports = tally;

Sprint-2/implement/tally.test.js

@@ -23,12 +23,27 @@ 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 counts duplicate items correctly", () => {
+  expect(tally(["a", "a", "b", "c", "b"])).toEqual({ a: 2, b: 2, c: 1 });
+});
 
 // Given an invalid input like a string
 // When passed to tally
 // Then it should throw an error
+test("tally throws an error when passed a string", () => {
+  expect(() => tally("hello")).toThrow();
+});
+
+// Given an array containing items named "toString"
+// When passed to tally
+// Then it should count them correctly without prototype interference
+test("tally correctly counts items named toString", () => {
+  expect(tally(["toString", "toString"])).toEqual({ toString: 2 });
+});

Sprint-2/interpret/invert.js

@@ -1,29 +1,45 @@
 // Let's define how invert should work
-
 // Given an object
 // When invert is passed this object
 // Then it should swap the keys and values in the object
 
-// E.g. invert({x : 10, y : 20}), target output: {"10": "x", "20": "y"}
+// E.g. invert({x: 10, y: 20}), target output: {"10": "x", "20": "y"}
+
+/*
+--- Answers to the Interpret Questions ---
+
+a) What is the return value of invert({a: 1}) in the old broken code?
+Answer: It returned { key: 1 } because dot notation (.key) creates a literal string key named "key".
+
+b) What is the return value of invert({a: 1, b: 2}) in the old broken code?
+Answer: It returned { key: 2 } because the literal property "key" is overwritten in the second loop iteration.
+
+c) What is the target return value of invert({a: 1, b: 2})?
+Answer: The target return value is { "1": "a", "2": "b" }.
+
+c-continued) What does Object.entries do? Why is it needed here?
+Answer: Object.entries(obj) converts the object into an array of key-value pairs, like [["a", 1], ["b", 2]]. It is needed because we cannot use a 'for...of' loop directly on a standard object.
+
+d) Why is the current return value different from the target?
+Answer: Because the old code used invertedObj.key (a hardcoded key name) instead of assigning the dynamic value as the new key.
 
+e) How can you fix it?
+Answer: By using bracket notation to set the 'value' as the new dynamic key, and assigning the 'key' as its value: invertedObj[value] = key;
+*/
+
+// Swap keys and values in an object
 function invert(obj) {
+  // Create an empty object to store the swapped pairs
   const invertedObj = {};
 
+  // Loop through each [key, value] pair in the original object
   for (const [key, value] of Object.entries(obj)) {
-    invertedObj.key = value;
+    // Use the VALUE as the new key, and the KEY as the new value
+    invertedObj[value] = key;
   }
 
+  // Return the inverted object
   return invertedObj;
 }
 
-// a) What is the current return value when invert is called with { a : 1 }
-
-// b) What is the current return value when invert is called with { a: 1, b: 2 }
-
-// c) What is the target return value when invert is called with {a : 1, b: 2}
-
-// c) What does Object.entries return? Why is it needed in this program?
-
-// d) Explain why the current return value is different from the target output
-
-// e) Fix the implementation of invert (and write tests to prove it's fixed!)
+module.exports = invert;