Birmingham | 26-ITP-May | Toluwalase Tiamiyu | Sprint 2 | Coursework

Sprint-2/debug/address.js

@@ -1,5 +1,10 @@
 // Predict and explain first...
 
+/* Prediction - the house number would return as undefined.
+
+Explaination - "address" is a plain javascript object, not an array, arrays make use of the numeric index positions like it was used in 
+the initial code but objects use key value pairs (properties) */
+
 // This code should log out the houseNumber from the address object
 // but it isn't working...
 // Fix anything that isn't working
@@ -12,4 +17,4 @@ 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

@@ -1,5 +1,11 @@
 // Predict and explain first...
 
+/* Prediction - TypeError: author is not iterable.
+
+Explaination - The "for... of" loop is designed fir iterable objects like arrays, strings, maps or sets,
+which have built in protocols. plain javascript objects like "author" are not iterable by default, 
+which would cause the error when the "for... of" loop is used. */
+
 // 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 +17,6 @@ const author = {
   alive: true,
 };
 
-for (const value of author) {
+for (const value of Object.Values(author)) {
   console.log(value);
 }

Sprint-2/debug/recipe.js

@@ -1,5 +1,11 @@
 // Predict and explain first...
 
+/* PREDICTION - it would print out the name, how many it serves perfectly but wouldn't work well for the ingredients.
+
+EXPLANATION
+Printing the whole object instead of ingredients: The template literal uses ${recipe} at the end. When JavaScript tries to insert an object into a template literal string, 
+it calls .toString() on the object, which results in the generic string "[object Object]" instead of showing its properties or the array inside. */
+
 // 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?
@@ -10,6 +16,5 @@ const recipe = {
   ingredients: ["olive oil", "tomatoes", "salt", "pepper"],
 };
 
-console.log(`${recipe.title} serves ${recipe.serves}
-  ingredients:
-${recipe}`);
+console.log(`${recipe.title} serves ${recipe.serves}\n
+ingredients:${recipe.ingredients.join("\n")}`);

Sprint-2/implement/contains.js

@@ -1,3 +1,8 @@
-function contains() {}
+function contains() {
+  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

@@ -20,16 +20,34 @@ 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");
+
+describe("contains()", () => {
+  test("returns false when given an empty object", () => {
+    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 the object contains the property name", () => {
+    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 the object does not contain the 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("returns false when passed invalid parameters like an array or primitive", () => {
+    expect(contains(["a", "b"], "0")).toBe(false);
+    expect(contains(null, "a")).toBe(false);
+    expect(contains("string", "length")).toBe(false);
+  });
+});

Sprint-2/implement/lookup.js

@@ -1,5 +1,8 @@
 function createLookup() {
-  // implementation here
+  if (!Array.isArray(countryCurrencyPairs)) {
+    return {};
+  }
+  return Object.fromEntries(countryCurrencyPairs);
 }
 
 module.exports = createLookup;

Sprint-2/implement/lookup.test.js

@@ -1,6 +1,30 @@
 const createLookup = require("./lookup.js");
 
-test.todo("creates a country currency code lookup for multiple codes");
+describe("createLookup()", () => {
+  test("creates a country currency code lookup for multiple codes", () => {
+    const input = [
+      ["US", "USD"],
+      ["CA", "CAD"],
+      ["GB", "GBP"],
+    ];
+    const expected = {
+      US: "USD",
+      CA: "CAD",
+      GB: "GBP",
+    };
+
+    expect(createLookup(input)).toEqual(expected);
+  });
+
+  test("returns an empty object when passed an empty array", () => {
+    expect(createLookup([])).toEqual({});
+  });
+
+  test("returns an empty object when passed invalid inputs", () => {
+    expect(createLookup(null)).toEqual({});
+    expect(createLookup("invalid")).toEqual({});
+  });
+});
 
 /*
 

Sprint-2/implement/querystring.js

@@ -1,16 +1,65 @@
 function parseQueryString(queryString) {
-  const queryParams = {};
-  if (queryString.length === 0) {
-    return queryParams;
+  const result = {};
+
+  // Return empty object for empty or non-string inputs
+  if (typeof queryString !== "string" || !queryString.trim()) {
+    return result;
   }
-  const keyValuePairs = queryString.split("&");
 
-  for (const pair of keyValuePairs) {
-    const [key, value] = pair.split("=");
-    queryParams[key] = value;
+  // Optional: strip leading '?' if passed a full URL search string (e.g., "?a=1")
+  const sanitizedInput = queryString.startsWith("?")
+    ? queryString.slice(1)
+    : queryString;
+
+  // Split pairs by '&'
+  const pairs = sanitizedInput.split("&");
+
+  for (const pair of pairs) {
+    // Ignore empty pairs (e.g. from consecutive '&&' or trailing '&')
+    if (!pair) continue;
+
+    // Find the FIRST '=' to separate key and value correctly
+    const equalIndex = pair.indexOf("=");
+
+    let rawKey = "";
+    let rawValue = "";
+
+    if (equalIndex === -1) {
+      // Key with no '=' (e.g., "key" -> key="key", value="")
+      rawKey = pair;
+      rawValue = "";
+    } else {
+      // Split strictly on the first '=' so values containing '=' stay intact
+      rawKey = pair.slice(0, equalIndex);
+      rawValue = pair.slice(equalIndex + 1);
+    }
+
+    // Helper to decode query string encoding (+ to space, percent-encoding)
+    const decodeParam = (str) => {
+      try {
+        return decodeURIComponent(str.replace(/\+/g, " "));
+      } catch {
+        // Fallback if URI decoding fails on malformed input
+        return str.replace(/\+/g, " ");
+      }
+    };
+
+    const key = decodeParam(rawKey);
+    const value = decodeParam(rawValue);
+
+    // Handle single key vs duplicate keys
+    if (Object.prototype.hasOwnProperty.call(result, key)) {
+      if (Array.isArray(result[key])) {
+        result[key].push(value);
+      } else {
+        result[key] = [result[key], value];
+      }
+    } else {
+      result[key] = value;
+    }
   }
 
-  return queryParams;
+  return result;
 }
 
 module.exports = parseQueryString;

Sprint-2/implement/querystring.test.js

@@ -3,7 +3,7 @@
 // Below are some test cases the implementation doesn't handle well.
 // Fix the implementation for these tests, and try to think of as many other edge cases as possible - write tests and fix those too.
 
-const parseQueryString = require("./querystring.js")
+const parseQueryString = require("./querystring.js");
 
 test("should parse values containing '='", () => {
   expect(parseQueryString("equation=a=b-2")).toEqual({
@@ -46,3 +46,21 @@ test("should store values of a key in an array when the key has 2 or more values
     foo: "bar",
   });
 });
+test("should strip leading '?' if present", () => {
+  expect(parseQueryString("?foo=bar&baz=qux")).toEqual({
+    foo: "bar",
+    baz: "qux",
+  });
+});
+
+test("should handle empty or invalid inputs gracefully", () => {
+  expect(parseQueryString("")).toEqual({});
+  expect(parseQueryString(null)).toEqual({});
+  expect(parseQueryString(undefined)).toEqual({});
+});
+
+test("should gracefully handle malformed percent encoding", () => {
+  expect(parseQueryString("key=%E0%A4")).toEqual({
+    key: "%E0%A4",
+  });
+});

Sprint-2/implement/tally.js

@@ -1,3 +1,12 @@
-function tally() {}
+function tally() {
+  if (!Array.isArray(items)) {
+    throw new TypeError("Input must be an array");
+  }
+  return items.reduce((acc, item) => {
+    // Increment count if key exists, otherwise initialize to 1
+    acc[item] = (acc[item] || 0) + 1;
+    return acc;
+  }, {});
+}
 
 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");
 
-// Given an array with duplicate items
-// When passed to tally
-// Then it should return counts for each unique item
+describe("tally()", () => {
+  test("tally on an empty array returns an empty object", () => {
+    expect(tally([])).toEqual({});
+  });
 
-// Given an invalid input like a string
-// When passed to tally
-// Then it should throw an error
+  // Given an array with duplicate items
+  // When passed to tally
+  // Then it should return counts for each unique item
+
+  test("returns counts for single and duplicate items", () => {
+    expect(tally(["a"])).toEqual({ a: 1 });
+    expect(tally(["a", "a", "a"])).toEqual({ a: 3 });
+    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("throws an error when passed invalid input like a string or null", () => {
+    expect(() => tally("a string")).toThrow(TypeError);
+    expect(() => tally(123)).toThrow(TypeError);
+    expect(() => tally(null)).toThrow(TypeError);
+  });
+});

Sprint-2/interpret/invert.js

@@ -5,6 +5,7 @@
 // Then it should swap the keys and values in the object
 
 // E.g. invert({x : 10, y : 20}), target output: {"10": "x", "20": "y"}
+/*
 
 function invert(obj) {
   const invertedObj = {};
@@ -15,15 +16,51 @@ function invert(obj) {
 
   return invertedObj;
 }
+*/
+/* a) What is the current return value when invert is called with { a : 1 }
 
-// a) What is the current return value when invert is called with { a : 1 }
+{ key: 1 }
 
 // b) What is the current return value when invert is called with { a: 1, b: 2 }
 
+{ key: 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?
+{ "1": "a", "2": "b" }
+// d) 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
+Object.entries(obj) returns an array of an object's own key-value pairs as [key, value] tuples (e.g., Object.entries({ a: 1, b: 2 }) returns [['a', 1], ['b', 2]]).
 
-// e) Fix the implementation of invert (and write tests to prove it's fixed!)
+It is needed here so we can loop over both the property name (key) and its corresponding value (value) at the same time using array destructuring (const [key, value]).
+
+// e) Explain why the current return value is different from the target output
+
+There are two critical issues in the current loop
+1. Static property assignment instead of dynamic lookup;
+The code writes invertedObj.key = value. Using dot notation literally creates/overwrites a single key named "key" on the object every single iteration. 
+To use the variable's value dynamically as the object key, you must use bracket notation: invertedObj[value].
+
+2. Flipped key and value;
+The target output asks to swap keys and values (so values become keys and keys become values). The original code assigns value to the object's key position, 
+rather than assigning key to the position indexed by value (invertedObj[value] = key). */
+
+// f) Fix the implementation of invert (and write tests to prove it's fixed!)
+
+function invert(obj) {
+  // Guard clause for non-object inputs
+  if (typeof obj !== "object" || obj === null || Array.isArray(obj)) {
+    return {};
+  }
+
+  const invertedObj = {};
+
+  for (const [key, value] of Object.entries(obj)) {
+    // Use bracket notation to dynamically set the property name to 'value'
+    // and assign 'key' as its value
+    invertedObj[value] = key;
+  }
+
+  return invertedObj;
+}
+
+module.exports = invert;

Sprint-2/interpret/invert.test.js

@@ -0,0 +1,22 @@
+const invert = require("./invert.js");
+
+describe("invert()", () => {
+  test("swaps keys and values for a single key-value pair", () => {
+    expect(invert({ a: 1 })).toEqual({ 1: "a" });
+  });
+
+  test("swaps keys and values for multiple key-value pairs", () => {
+    expect(invert({ x: 10, y: 20 })).toEqual({ 10: "x", 20: "y" });
+    expect(invert({ a: "1", b: "2" })).toEqual({ 1: "a", 2: "b" });
+  });
+
+  test("handles empty objects", () => {
+    expect(invert({})).toEqual({});
+  });
+
+  test("handles non-object invalid inputs gracefully", () => {
+    expect(invert(null)).toEqual({});
+    expect(invert(["a", "b"])).toEqual({});
+    expect(invert("string")).toEqual({});
+  });
+});