Birmingham | 26-ITP-May | Ogbemi Mene | Sprint 2 | Module data groups/sprint2

Sprint-2/debug/address.js

@@ -12,4 +12,4 @@ 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 +3,26 @@
 // 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
 
+//const author = {
+  //firstName: "Zadie",
+  //lastName: "Smith",
+  //occupation: "writer",
+  //age: 40,
+  //alive: true,
+//};
+
+//for (const value of author) {
+  //console.log(value);
+//}
+
+// If you run this snippet, JavaScript will throw a TypeError: author is not iterable.
+// The for...of loop is designed specifically for iterable objects (like Arrays, Strings, Sets, or Maps)
+// Plain JavaScript objects ({}) are not iterable by default with for...of.
+// They are collection of key-value pairs without a guaranteed built-in iteration order sequence.
+
+// to fix this, i wii specifically want to stick with for...of to loop directly through the property values:
+// i will use Object.values() with for...of
+
 const author = {
   firstName: "Zadie",
   lastName: "Smith",
@@ -11,6 +31,7 @@ const author = {
   alive: true,
 };
 
-for (const value of author) {
+// Object.values(author) returns an array: ["Zadie", "Smith", "writer", 40, true]
+for (const value of Object.values(author)) {
   console.log(value);
-}
+}

Sprint-2/debug/recipe.js

@@ -13,3 +13,26 @@ const recipe = {
 console.log(`${recipe.title} serves ${recipe.serves}
   ingredients:
 ${recipe}`);
+
+// Predict and explain
+// Two things are going wrong here:
+
+//Printing the whole object instead of individual pieces: At the very end,
+// ${recipe} tries to drop the entire recipe object into the text string.
+// When JavaScript tries to turn a plain object into text like that, it defaults to printing [object Object].
+//Ingredients are not separated: The code doesn't include a loop or a tool to extract the ingredients array and put each item on its own new line.
+
+// we can fix this code by argeting the specific properties of the object (recipe.title, recipe.serves) and using the .join("\n") method on the ingredients array.
+// The .join("\n") method takes a list and glues the items together using a newline character (\n), which forces each ingredient onto its own line.
+
+// so here is the correct code to fix it
+const recipe = {
+  title: "bruschetta",
+  serves: 2,
+  ingredients: ["olive oil", "tomatoes", "salt", "pepper"],
+};
+
+// Use .join("\n") to separate each ingredient with a new line
+console.log(`${recipe.title} serves ${recipe.serves}
+ingredients:
+${recipe.ingredients.join("\n")}`);

Sprint-2/implement/contains.js

@@ -1,3 +1,11 @@
-function contains() {}
+function contains(obj, prop) {
+  // Guard clause: Ensure obj is a valid, non-null, non-array object
+  if (typeof obj !== "object" || obj === null || Array.isArray(obj)) {
+    return false;
+  }
+
+  // Check if the object directly holds the specified key
+  return Object.hasOwn(obj, prop);
+}
 
 module.exports = contains;

Sprint-2/implement/contains.test.js

@@ -33,3 +33,23 @@ test.todo("contains on empty object returns false");
 // Given invalid parameters like an array
 // When passed to contains
 // Then it should return false or throw an error
+
+describe("contains", () => {
+  test("returns false for an empty object", () => {
+    expect(contains({}, "a")).toBe(false);
+  });
+
+  test("returns true for an existing property name", () => {
+    expect(contains({ a: 1, b: 2 }, "a")).toBe(true);
+  });
+
+  test("returns false for a non-existent property name", () => {
+    expect(contains({ a: 1, b: 2 }, "c")).toBe(false);
+  });
+
+  test("returns false when given invalid parameters (e.g. array, null, primitive)", () => {
+    expect(contains([1, 2, 3], "0")).toBe(false);
+    expect(contains(null, "a")).toBe(false);
+    expect(contains("not an object", "a")).toBe(false);
+  });
+});

Sprint-2/implement/lookup.js

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

Sprint-2/implement/lookup.test.js

@@ -33,3 +33,20 @@ It should return:
    'CA': 'CAD'
  }
 */
+
+
+test("creates a country currency code lookup for multiple codes", () => {
+  const input = [
+    ["US", "USD"],
+    ["CA", "CAD"],
+    ["GB", "GBP"],
+  ];
+
+  const expectedOutput = {
+    US: "USD",
+    CA: "CAD",
+    GB: "GBP",
+  };
+
+  expect(createLookup(input)).toEqual(expectedOutput);
+});

Sprint-2/implement/querystring.js

@@ -1,16 +1,54 @@
 function parseQueryString(queryString) {
-  const queryParams = {};
-  if (queryString.length === 0) {
-    return queryParams;
+  const result = {};
+
+  if (!queryString) return result;
+  if (queryString.startsWith("?")) {
+    queryString = queryString.slice(1);
   }
-  const keyValuePairs = queryString.split("&");
 
-  for (const pair of keyValuePairs) {
-    const [key, value] = pair.split("=");
-    queryParams[key] = value;
+  const decode = (str) => {
+    try {
+      return decodeURIComponent(str.replace(/\+/g, " "));
+    } catch {
+      return str;
+    }
+  };
+
+  const pairs = queryString.split("&");
+
+  for (const pair of pairs) {
+    if (!pair) continue;
+
+    const equalIndex = pair.indexOf("=");
+    let rawKey, rawValue;
+
+    if (equalIndex === -1) {
+      rawKey = pair;
+      rawValue = "";
+    } else {
+      rawKey = pair.slice(0, equalIndex);
+      rawValue = pair.slice(equalIndex + 1);
+    }
+
+    const key = decode(rawKey);
+    const value = decode(rawValue);
+
+    // Safeguard against prototype pollution while setting keys safely
+    if (!Object.hasOwn(result, key)) {
+      Object.defineProperty(result, key, {
+        value: value,
+        writable: true,
+        enumerable: true,
+        configurable: true,
+      });
+    } else if (Array.isArray(result[key])) {
+      result[key].push(value);
+    } else {
+      result[key] = [result[key], value];
+    }
   }
 
-  return queryParams;
+  return result;
 }
 
 module.exports = parseQueryString;

Sprint-2/implement/querystring.test.js

@@ -46,3 +46,30 @@ test("should store values of a key in an array when the key has 2 or more values
     foo: "bar",
   });
 });
+
+
+describe("parseQueryString additional edge cases", () => {
+  test("should strip leading '?' if present", () => {
+    expect(parseQueryString("?foo=bar&baz=qux")).toEqual({
+      foo: "bar",
+      baz: "qux",
+    });
+  });
+
+  test("should handle empty or missing query string safely", () => {
+    expect(parseQueryString("")).toEqual({});
+    expect(parseQueryString(null)).toEqual({});
+  });
+
+  test("should prevent prototype pollution from '__proto__' keys", () => {
+    const result = parseQueryString("__proto__=polluted");
+    expect(Object.prototype.polluted).toBeUndefined();
+    expect(result["__proto__"]).toBe("polluted");
+  });
+
+  test("should gracefully fallback on malformed percent encoding", () => {
+    expect(parseQueryString("key=%E0%A4")).toEqual({
+      key: "%E0%A4",
+    });
+  });
+});

Sprint-2/implement/tally.js

@@ -1,3 +1,17 @@
-function tally() {}
+function tally(items) {
+  // Guard clause: Ensure input is strictly an array
+  if (!Array.isArray(items)) {
+    throw new TypeError("Input must be an array");
+  }
+
+  const counts = {};
+
+  for (const item of items) {
+    // Safely increment count or initialize to 1
+    counts[item] = (counts[item] || 0) + 1;
+  }
+
+  return counts;
+}
 
 module.exports = tally;

Sprint-2/implement/tally.test.js

@@ -32,3 +32,19 @@ test.todo("tally on an empty array returns an empty object");
 // Given an invalid input like a string
 // When passed to tally
 // Then it should throw an error
+
+describe("tally", () => {
+  test("tally on an empty array returns an empty object", () => {
+    expect(tally([])).toEqual({});
+  });
+
+  test("returns counts for unique items", () => {
+    expect(tally(["a", "a", "b", "c"])).toEqual({ a: 2, b: 1, c: 1 });
+  });
+
+  test("throws an error when passed invalid input like a string", () => {
+    expect(() => tally("not an array")).toThrow(TypeError);
+    expect(() => tally(123)).toThrow(TypeError);
+    expect(() => tally(null)).toThrow(TypeError);
+  });
+});

Sprint-2/interpret/invert.js

@@ -27,3 +27,50 @@ function invert(obj) {
 // 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!)
+
+// this are the answers:
+
+// a) Return value for { a: 1 }
+// { key: 1 }
+
+// b) Return value for { a: 1, b: 2 }
+// { key: 2 }
+
+// c1) Target return value for { a: 1, b: 2 }
+// { "1": "a", "2": "b" }
+
+// c2) What does Object.entries return? Why is it needed?
+// What it returns: An array of key-value pairs (as two-element arrays), e.g., [["a", 1], ["b", 2]].
+// Why it’s needed: It lets us easily loop through both keys and values at the same time using for (const [key, value] of Object.entries(obj)).
+
+// d) Why the current return value is different from target output
+// The line invertedObj.key = value; uses dot notation, which treats "key" as a literal property name on the object instead of using the variable key.
+
+// Furthermore, to invert the object, the value needs to become the new key and the old key needs to become the new value.
+
+// Because dot notation was used:
+
+// Every loop iteration overwrote invertedObj["key"] with the variable value.
+
+// The key/value assignment was backwards.
+
+// e) Fixed Implementation & Tests
+// Fixed invert.js
+// Use bracket notation [value] to dynamically set the property name:
+
+function invert(obj) {
+  // Guard clause for safety
+  if (typeof obj !== "object" || obj === null || Array.isArray(obj)) {
+    return {};
+  }
+
+  const invertedObj = {};
+
+  for (const [key, value] of Object.entries(obj)) {
+    invertedObj[value] = key;
+  }
+
+  return invertedObj;
+}
+
+

Sprint-2/stretch/count-words.js

@@ -26,3 +26,35 @@
 
 3. Order the results to find out which word is the most common in the input
 */
+
+function countWordsAdvanced(str) {
+  if (!str.trim()) return {};
+
+  // 1 & 2: Convert to lowercase and strip punctuation using Regex
+  const cleanedStr = str
+    .toLowerCase()
+    .replace(/[^\w\s]|_/g, ""); // Removes punctuation like .,!?- etc.
+
+  // Match words, splitting on whitespace
+  const words = cleanedStr.match(/\b\w+\b/g);
+  if (!words) return {};
+
+  const wordCounts = {};
+
+  for (let i = 0; i < words.length; i++) {
+    const word = words[i];
+    wordCounts[word] = (wordCounts[word] || 0) + 1;
+  }
+
+  // 3: Sort the result by frequency (most common first)
+  const sortedEntries = Object.entries(wordCounts).sort(
+    (a, b) => b[1] - a[1]
+  );
+
+  // Convert back into an object (maintains insertion order in modern JavaScript)
+  return Object.fromEntries(sortedEntries);
+}
+
+// Example usage:
+console.log(countWordsAdvanced("You and me! And you, and ME..."));
+// Output: { and: 3, you: 2, me: 2 }