London | ITP-May-2025 | Sisay Mehari | Module-Data-Groups | Sprint 2

Sprint-2/debug/address.js

@@ -1,4 +1,9 @@
 // Predict and explain first...
+// address is an object.
+// JavaScript objects don’t have numeric indices like arrays do 
+// Or we have a key like "0".
+
+
 
 // This code should log out the houseNumber from the address object
 // but it isn't working...
@@ -12,4 +17,6 @@ const address = {
   postcode: "XYZ 123",
 };
 
-console.log(`My house number is ${address[0]}`);
+console.log(`My house number is ${address["houseNumber"]}`);
+console.log(`My house number is ${address.houseNumber}`);
+

Sprint-2/debug/author.js

@@ -1,5 +1,6 @@
 // Predict and explain first...
-
+//author is a plain object, and JavaScript's for...of loop only works with iterable data types (like arrays, strings, etc.). Plain objects aren’t iterable
+// we use Object.values(obj) to get property of values
 // 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 +12,6 @@ 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 +1,6 @@
 // Predict and explain first...
+//recipe is an object, and when w insert an object directly into a string (like ${recipe}), 
+// javaScript converts it to a string using toString()
 
 // This program should log out the title, how many it serves and the ingredients.
 // Each ingredient should be logged on a new line
@@ -12,4 +14,4 @@ const recipe = {
 
 console.log(`${recipe.title} serves ${recipe.serves}
   ingredients:
-${recipe}`);
+${recipe.ingredients.join("\n")}`);

Sprint-2/implement/contains.js

@@ -1,3 +1,8 @@
-function contains() {}
+function contains(object, key) {
+    if (typeof object !== "object" || object === null || Array.isArray(object)) {
+        throw new Error("Invalid input: expected an object");
+    } 
+    return object.hasOwnProperty(key);
+}
 
 module.exports = contains;

Sprint-2/implement/contains.test.js

@@ -16,20 +16,33 @@ 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("contains with an existing property name returns true", () => {
+    expect(contains ({a: 1, b: 2}, "a")).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);
+});
 
 // Given an object with properties
 // When passed to contains with an existing property name
 // Then it should return true
+test("contains with an existing property name", () => {
+    expect(contains({a: 1, b: 2}, "b")).toBe(true);
+});
 
 // Given an object with properties
 // When passed to contains with a non-existent property name
 // Then it should return false
+test("contains with a non-existent property name", () => {
+  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 throws an error for invalid input like an array", () => {
+    expect(() => contains(["a", "b"], "a")).toThrow("Invalid input: expected an object");
+});

Sprint-2/implement/lookup.js

@@ -1,5 +1,7 @@
-function createLookup() {
+function createLookup(key, value) {
+  return Object.fromEntries(key, value);
   // implementation here
+
 }
 
 module.exports = createLookup;

Sprint-2/implement/lookup.test.js

@@ -1,6 +1,10 @@
 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']];
+  const expectedOutput = { US : 'USD', CA: 'CAD' };
+  expect(createLookup(input)).toEqual(expectedOutput);
+});
 
 /*
 

Sprint-2/implement/querystring.js

@@ -6,11 +6,20 @@ function parseQueryString(queryString) {
   const keyValuePairs = queryString.split("&");
 
   for (const pair of keyValuePairs) {
-    const [key, value] = pair.split("=");
+    const [key, ...rest] = pair.split("=");
+    const value = rest.join("=");
+    if (queryParams.hasOwnProperty(key)) {
+      if (!Array.isArray(queryParams[key])) {
+        queryParams[key] = [queryParams[key]];
+      }
+      queryParams[key].push(value);
+    } else {
     queryParams[key] = value;
+    }
   }
 
   return queryParams;
 }
 
+
 module.exports = parseQueryString;

Sprint-2/implement/querystring.test.js

@@ -10,3 +10,28 @@ test("parses querystring values containing =", () => {
     "equation": "x=y+1",
   });
 });
+
+test("parses querystring with multiple values", () => {
+  expect(parseQueryString("a=1&b=2=c")).toEqual({
+    "a": "1",
+    "b": "2=c",
+  });
+});
+test("parses querystring Multiple values for the same key", () =>{
+  expect(parseQueryString("category=books&category=movies&category=music")).toEqual({
+    "category": ["books", "movies", "music"]
+  })
+});
+test("parses querystring with empty values", () => {
+  expect(parseQueryString("username=")).toEqual({
+    username: ""
+  });
+});
+test("parses querystring key with no values", () => {
+  expect(parseQueryString("hello=")).toEqual({ hello: "" });
+});
+test ("parses querystring with no equal sign", () => {
+  expect(parseQueryString("bye")).toEqual({
+    bye: ""
+  });
+});

Sprint-2/implement/tally.js

@@ -1,3 +1,11 @@
-function tally() {}
+function tally(items) {
+    if (!Array.isArray(items)) {
+        throw new Error("Invalid input: expected an array");
+    }
+    return items.reduce((acc, item) => {
+        acc[item] = (acc[item] || 0) + 1;
+        return acc;
+    }, {});
+}
 
 module.exports = tally;

Sprint-2/implement/tally.test.js

@@ -19,16 +19,27 @@ 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 with a single item returns count of 1", () => {
+    expect(tally(['a'])).toEqual({ a: 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 with duplicate items returns correct counts", () => {
+    expect(tally(['a', 'a', 'b', 'c'])).toEqual({ a: 2, b: 1, c: 1 });
+});
 
 // 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 like a string", () => {
+    expect(() => tally("not an array")).toThrow("Invalid input: expected an array");
+});

Sprint-2/interpret/invert.js

@@ -10,20 +10,38 @@ function invert(obj) {
   const invertedObj = {};
 
   for (const [key, value] of Object.entries(obj)) {
-    invertedObj.key = value;
+    // invertedObj.key = value;
+    invertedObj[value] = key;
   }
 
   return invertedObj;
 }
+console.log(invert({ a: 1, b: 2 }));
 
 // a) What is the current return value when invert is called with { a : 1 }
+// Object.entries({ a: 1 })  gives [['a', 1]]
+// so in the loop key = "a", value = 1
+// the line invertedObj.key = value;  it adds a property with the key "key"  rather than using the variable key.
+// { key: 1 }
 
 // b) What is the current return value when invert is called with { a: 1, b: 2 }
+// {key: 2} it overwrites the previous value of key
+
 
 // c) What is the target return value when invert is called with {a : 1, b: 2}
+// we want to change the position of the key and value
+// {"1": "a", "2": "b}
 
 // c) What does Object.entries return? Why is it needed in this program?
+// it returns the object in to array
+// Object.entries ({a: 1, b: 2}) returns 
+// [["a", 1], ["b", 2]]
 
 // d) Explain why the current return value is different from the target output
+// this line invertedObj.key = value; 
+// it is not using the key variable it is adding a property named key.
 
 // e) Fix the implementation of invert (and write tests to prove it's fixed!)
+
+
+module.exports = invert;

Sprint-2/interpret/invert.test.js

@@ -0,0 +1,24 @@
+const invert = require('./invert');
+test('invert  a single key-value pair', () => {
+    expect(invert({ a: 1 })).toEqual({ '1': 'a' });
+});
+
+
+test('invert multiple key-value pairs', () => {
+    expect(invert({ a: 1, b: 2 })).toEqual({ '1': 'a', '2': 'b' });
+});
+
+
+test("invert string value as key input ", () => {
+    expect(invert({ a: "apple", b: "banana" })).toEqual({ apple: "a", banana: "b" });
+});
+
+
+test ("returns empty object when input is empty", () => {
+    expect(invert({})).toEqual({});
+});
+
+test("invert with numeric keys", () => {
+    expect(invert({ 1: 'one', 2: 'two' })).toEqual({ one: '1', two: '2' });
+});
+

Sprint-2/stretch/count-words.js

@@ -26,3 +26,17 @@
 
 3. Order the results to find out which word is the most common in the input
 */
+function countWords(str) {
+  const cleanStr = str.replace(/[.,!?]/g, "").toLowerCase();
+  const words = cleanStr.split(" ");
+  const count  = words.reduce((acc, word) => {
+    acc[word] = (acc[word] || 0) + 1;
+    return acc;
+  }, {});
+  const sorted = Object.entries(count).sort((a, b) => b[1] - a[1]);
+  return sorted;
+}
+
+
+console.log(countWords("you and me and you"));
+

Sprint-2/stretch/mode.js

@@ -8,22 +8,21 @@
 // refactor calculateMode by splitting up the code
 // into smaller functions using the stages above
 
-function calculateMode(list) {
   // track frequency of each value
-  let freqs = new Map();
-
-  for (let num of list) {
-    if (typeof num !== "number") {
-      continue;
+  function getFrequencies(list) {
+    const freq = new Map();
+    for (let num of list) {
+      if (typeof num !== "number") continue;
+      freq.set(num, (freq.get(num) || 0) + 1);
     }
-
-    freqs.set(num, (freqs.get(num) || 0) + 1);
+    return freq;
   }
 
   // Find the value with the highest frequency
+  function getMode(freqMap) {
   let maxFreq = 0;
   let mode;
-  for (let [num, freq] of freqs) {
+  for (let [num, freq] of freqMap) {
     if (freq > maxFreq) {
       mode = num;
       maxFreq = freq;
@@ -32,5 +31,8 @@ function calculateMode(list) {
 
   return maxFreq === 0 ? NaN : mode;
 }
-
+  function calculateMode(list) {
+    const freq = getFrequencies(list);
+    return getMode(freq);
+}
 module.exports = calculateMode;

Sprint-2/stretch/till.js

@@ -8,10 +8,14 @@ function totalTill(till) {
   let total = 0;
 
   for (const [coin, quantity] of Object.entries(till)) {
-    total += coin * quantity;
+    const coinValue = parseInt(coin); 
+    if (isNaN(coinValue)) {
+      continue;
+    }
+    total += coinValue * quantity;
   }
 
-  return `£${total / 100}`;
+  return `£${(total / 100).toFixed(2)}`;
 }
 
 const till = {
@@ -21,11 +25,21 @@ const till = {
   "20p": 10,
 };
 const totalAmount = totalTill(till);
+console.log(totalAmount);
+module.exports = totalTill; 
 
 // a) What is the target output when totalTill is called with the till object
+// 10p + 30p + 200p + 200p = 440p → £4.40  so the target output is "£4.40"
 
 // b) Why do we need to use Object.entries inside the for...of loop in this function?
+// because till os an object and if we use Object.entries, it will return an array of key-value pairs.
+// if we don't use Object.entries, we would either get the keys (with Object.keys) or only the values (with object.values), but not both
 
 // c) What does coin * quantity evaluate to inside the for...of loop?
-
+//The expression coin * quantity tries to multiply a string (coin) by a number (quantity).
+// so coin * quantity evaluates to NaN because coin is a string like "50p", and JavaScript cannot multiply a non-numeric string by a number.
+// to fix that we need to extract the number from "50p"
+// parseInt(coin) will convert the string "50p" to 50, and then we can multiply it by quantity.
+// total += parseInt(coin) * quantity;
 // d) Write a test for this function to check it works and then fix the implementation of totalTill
+