Manchester | 26-ITP-Sep | Salah Alsabhi | Sprint 2 | Complete Sprint 2 exercises

Sprint-2/debug/address.js

@@ -12,4 +12,9 @@ const address = {
   postcode: "XYZ 123",
 };
 
-console.log(`My house number is ${address[0]}`);
+console.log(`My house number is ${address.houseNumber}`);
+
+
+/* BUG: address[0] is undefined because objects aren't indexed by number.
+ FIX: useed the property name: address.houseNumber
+console.log(`My house number is ${address.houseNumber}`);

Sprint-2/debug/author.js

@@ -11,6 +11,14 @@ const author = {
   alive: true,
 };
 
-for (const value of author) {
+for (const value of Object.values(author)) {
   console.log(value);
 }
+
+
+/* BUG: Objects are not iterable, so `for...of author` throws TypeError.
+ FIX: Used Object.values(author) to loop over the property values.
+for (const value of Object.values(author)) {
+  console.log(value);
+}
+*/

Sprint-2/debug/recipe.js

@@ -12,4 +12,10 @@ const recipe = {
 
 console.log(`${recipe.title} serves ${recipe.serves}
   ingredients:
-${recipe}`);
+${recipe.ingredients.join("\n")}`);
+
+
+
+// BUG: ${recipe} logs out the whole object as "[object Object]".
+// FIX: print title/serves from their properties, and ingredients with join("\n")
+// so each item is on its own line.

Sprint-2/implement/contains.js

@@ -1,3 +1,9 @@
-function contains() {}
+function contains(obj, prop) {
+  if (obj === null || typeof obj !== "object" || Array.isArray(obj)) {
+    throw new Error("contains requires an object");
+  }
+  return Object.hasOwn(obj, prop);
+}
 
 module.exports = contains;
+

Sprint-2/implement/contains.test.js

@@ -23,18 +23,50 @@ as an array isn't an object
 // 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("returns true when property exists", () => {
+  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("returns false when property does not exist", () => {
+  expect(contains({ a: 1, b: 2 }, "c")).toBe(false);
+});
 
 // Given a value that isn't an object - an array, a string, a number,
 // null, or no argument at all
 // When passed to contains
 // Then it should throw Error("contains requires an object")
 // (careful: typeof [] and typeof null are both "object")
+
+test("throws an error when given an array", () => {
+  expect(() => contains([3, 4, 5], "a")).toThrow(
+    new Error("contains requires an object")
+  );
+});
+
+test("throws an error when given a null", () => {
+  expect(() => contains(null, "a")).toThrow(
+    new Error("contains requires an object")
+  );
+});
+
+test("throws an error when given a string", () => {
+  expect(() => contains("hellow", "a")).toThrow(
+    new Error("contains requires an object")
+  );
+});
+
+test("throws an error when given no argument", () => {
+  expect(() => contains()).toThrow(
+    new Error("contains requires an object")
+  );
+});

Sprint-2/implement/lookup.js

@@ -1,5 +1,10 @@
-function createLookup() {
-  // implementation here
+
+function createLookup(pairs) {
+  const lookup = {};
+  for (const [country, currency] of pairs) {
+    lookup[country] = currency;
+  }
+  return lookup;
 }
 
 module.exports = createLookup;

Sprint-2/implement/lookup.test.js

@@ -1,6 +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" });
+});
 
 /*
 

Sprint-2/implement/querystring.js

@@ -1,16 +1,46 @@
 function parseQueryString(queryString) {
   const queryParams = {};
+
   if (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;
+    }
+
+    const eqIndex = pair.indexOf("=");
+    let key;
+    let value;
+
+    if (eqIndex === -1) {
+      key = pair;
+      value = "";
+    } else {
+      key = pair.slice(0, eqIndex);
+      value = pair.slice(eqIndex + 1);
+    }
+
+    key = decodeURIComponent(key.replaceAll("+", " "));
+    value = decodeURIComponent(value.replaceAll("+", " "));
+
+    if (Object.hasOwn(queryParams, key)) {
+      if (Array.isArray(queryParams[key])) {
+        queryParams[key].push(value);
+      } else {
+        queryParams[key] = [queryParams[key], value];
+      }
+    } else {
+      queryParams[key] = value;
+    }
   }
 
   return queryParams;
 }
 
 module.exports = parseQueryString;
+
+

Sprint-2/implement/tally.js

@@ -1,3 +1,12 @@
-function tally() {}
+function tally(items) {
+  if (!Array.isArray(items)) {
+    throw new Error("tally requires an array");
+  }
+  const counts = {};
+  for (const item of items) {
+    counts[item] = (counts[item] ?? 0) + 1;
+  }
+  return counts;
+}
 
 module.exports = tally;

Sprint-2/implement/tally.test.js

@@ -23,12 +23,29 @@ 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 on an array with duplicate items, return counts for each unique item", () => {
+  expect(tally(["a", "a", "c", "b", "c", "b", "c", "e"])).toEqual({ a: 2, c: 3, b: 2, e: 1 });
+});
 
 // Given an invalid input like a string, a number, or no argument at all
 // When passed to tally
 // Then it should throw Error("tally requires an array")
+test("tally on a string, thows an error", () => {
+  expect(() => tally("hello")).toThrow(new Error("tally requires an array"));
+});
+
+test("tally on a number, thows an error", () => {
+  expect(() => tally(10)).toThrow(new Error("tally requires an array"));
+});
+
+test("tally on no argument, thows an error", () => {
+  expect(() => tally()).toThrow(new Error("tally requires an array"));
+});
+

Sprint-2/interpret/invert.js

@@ -6,24 +6,46 @@
 
 // E.g. invert({x : 10, y : 20}), target output: {"10": "x", "20": "y"}
 
-function invert(obj) {
+export 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 for invert({ a: 1 }) with the OLD bug:
+   { key: 1 }
+
+b) Current return value for invert({ a: 1, b: 2 }) with the OLD bug:
+   { key: 2 }
+   (each loop overwrites the same property named "key"; last value wins)
+
+c) Target return value for invert({ a: 1, b: 2 }):
+   { "1": "a", "2": "b" }
+
+Object.entries returns an array of [key, value] pairs for the object.
+It is needed so the loop can read both the key and the value of each property.
+
+d) invertedObj.key always writes to a property literally named "key".
+   It ignores the loop variable `key`, so keys and values are never swapped,
+   and earlier entries are overwritten. The result is a new object with only
+   that one "key" property — not the original object, and not an inverted map.
+
+e) Fixed by using invertedObj[value] = key (bracket notation with the value
+   as the new key). Tests in invert.test.js prove the fix.
+*/
+
+
+
+
+
+
 
-// 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!)

Sprint-2/stretch/count-words.js

@@ -26,3 +26,24 @@
 
 3. Order the results to find out which word is the most common in the input
 */
+
+function countWords(str) {
+  const counts = {};
+  if (str.trim() === "") {
+    return counts;
+  }
+
+  const words = str
+    .toLowerCase() 
+    .replaceAll(/[.,!?]/g, "") 
+    .split(/\s+/)
+    .filter((w) => w.length > 0);
+
+  for (const word of words) {
+    counts[word] = (counts[word] ?? 0) + 1;
+  }
+
+  return counts;
+}
+
+module.exports = countWords;

Sprint-2/stretch/mode.js

@@ -12,8 +12,7 @@
 
 // The tests must still pass after your refactor. Run them again to check.
 
-function calculateMode(list) {
-  // check the input is a non-empty array of numbers
+function assertValidNumbers(list) {
   if (!Array.isArray(list)) {
     throw new Error("calculateMode requires an array of numbers");
   }
@@ -25,25 +24,32 @@ function calculateMode(list) {
       throw new Error("calculateMode requires an array of numbers");
     }
   }
+}
 
-  // track frequency of each value
-  let freqs = new Map();
-
-  for (let num of list) {
+function trackFrequencies(list) {
+  const freqs = new Map();
+  for (const num of list) {
     freqs.set(num, (freqs.get(num) || 0) + 1);
   }
+  return freqs;
+}
 
-  // Find the value with the highest frequency
+function findMode(freqs) {
   let maxFreq = 0;
   let mode;
-  for (let [num, freq] of freqs) {
+  for (const [num, freq] of freqs) {
     if (freq > maxFreq) {
       mode = num;
       maxFreq = freq;
     }
   }
-
   return mode;
 }
 
+function calculateMode(list) {
+  assertValidNumbers(list);
+  const freqs = trackFrequencies(list);
+  return findMode(freqs);
+}
+
 module.exports = calculateMode;