London | ITP-Sept-2025 | Mariia Serhiienko | Sprint 2 | Module Data Groups

Sprint-2/debug/address.js

@@ -1,4 +1,7 @@
 // Predict and explain first...
+//I guess that the code will log "My house number is undefined" because address[0] isn't a valid way
+// to access the houseNumber property. When we do address[0], JS looks for a property literally
+// named "0", because bracket notation treats 0 as the string "0"
 
 // This code should log out the houseNumber from the address object
 // but it isn't working...
@@ -12,4 +15,4 @@ 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

@@ -1,4 +1,6 @@
 // Predict and explain first...
+// for...of only works on arrays. An object isn’t an array, so we can’t loop over it directly.
+// To find values from the object we need to convert it to an array of values 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
@@ -11,6 +13,6 @@ 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...
+// I think it incorrectly tries to log ingredients - this should be an array,
+// but there's missed .ingredients after the object name, so it will likely log something like "[object Object]" instead of the actual ingredients.
 
 // 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(", ")}`);

Sprint-2/implement/contains.js

@@ -1,3 +1,6 @@
-function contains() {}
+function contains(obj, prop) {
+  if (Object.keys(obj).length === 0) return false;
+  return Object.prototype.hasOwnProperty.call(obj, prop);
+}
 
 module.exports = contains;

Sprint-2/implement/contains.test.js

@@ -17,19 +17,32 @@ as the object doesn't contains a key of 'c'
 // When passed an object and a property name
 // Then it should return true if the object contains the property, false otherwise
 
-// Given an empty object
-// When passed to contains
-// Then it should return false
-test.todo("contains on empty object returns false");
-
-// Given an object with properties
-// When passed to contains with an existing property name
-// Then it should return true
-
-// Given an object with properties
-// When passed to contains with a non-existent property name
-// Then it should return false
-
-// Given invalid parameters like an array
-// When passed to contains
-// Then it should return false or throw an error
+describe("contains", () => {
+  // Given an empty object
+  // When passed to contains
+  // Then it should return 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 on object with existing property returns true", () => {
+    expect(contains({ a: 1, d: 4 }, "d")).toBe(true);
+  });
+
+  // Given an object with properties
+  // When passed to contains with a non-existent property name
+  // Then it should return false
+  test("contains on object with non-existent property returns false", () => {
+    expect(contains({ a: 1, b: 4 }, "c")).toBe(false);
+  });
+
+  // Given invalid parameters like an array
+  // When passed to contains
+  // Then it should return false or throw an error
+  test("contains on invalid parameters returns false", () => {
+    expect(contains([], "a")).toBe(false);
+  });
+});

Sprint-2/implement/lookup.js

@@ -1,5 +1,9 @@
-function createLookup() {
-  // implementation here
+function createLookup(arr) {
+  const lookup = {};
+  for (const [country, currency] of arr) {
+    lookup[country] = currency;
+  }
+  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 +31,42 @@ It should return:
    'CA': 'CAD'
  }
 */
+
+describe("createLookup", () => {
+  test("should create a lookup object from country-currency pairs", () => {
+    const countryCurrencyPairs = [
+      ["US", "USD"],
+      ["CA", "CAD"],
+      ["GB", "GBP"],
+      ["FR", "EUR"],
+    ];
+
+    const expectedLookup = {
+      US: "USD",
+      CA: "CAD",
+      GB: "GBP",
+      FR: "EUR",
+    };
+
+    const lookup = createLookup(countryCurrencyPairs);
+    expect(lookup).toEqual(expectedLookup);
+  });
+
+  test("should return an empty object when given an empty array", () => {
+    const countryCurrencyPairs = [];
+    const expectedLookup = {};
+
+    const lookup = createLookup(countryCurrencyPairs);
+    expect(lookup).toEqual(expectedLookup);
+  });
+
+  test("should handle single pair correctly", () => {
+    const countryCurrencyPairs = [["CA", "CAD"]];
+    const expectedLookup = {
+      CA: "CAD",
+    };
+
+    const lookup = createLookup(countryCurrencyPairs);
+    expect(lookup).toEqual(expectedLookup);
+  });
+});

Sprint-2/implement/querystring.js

@@ -6,8 +6,8 @@ function parseQueryString(queryString) {
   const keyValuePairs = queryString.split("&");
 
   for (const pair of keyValuePairs) {
-    const [key, value] = pair.split("=");
-    queryParams[key] = value;
+    const [key, ...rest] = pair.split("=");
+    queryParams[key] = rest.join("=");
   }
 
   return queryParams;

Sprint-2/implement/querystring.test.js

@@ -3,10 +3,37 @@
 // Below is one test case for an edge case the implementation doesn't handle well.
 // Fix the implementation for this test, 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("parses querystring values containing =", () => {
-  expect(parseQueryString("equation=x=y+1")).toEqual({
-    "equation": "x=y+1",
+describe("parseQueryString", () => {
+  test("parses querystring values containing =", () => {
+    expect(parseQueryString("equation=x=y+1")).toEqual({
+      equation: "x=y+1",
+    });
+  });
+
+  test("parses empty querystring", () => {
+    expect(parseQueryString("")).toEqual({});
+  });
+
+  test("parses multiple key-value pairs", () => {
+    expect(parseQueryString("name=Jane&age=37&city=New+York")).toEqual({
+      name: "Jane",
+      age: "37",
+      city: "New+York",
+    });
+  });
+
+  test("parses key with empty value", () => {
+    expect(parseQueryString("key1=&key2=value2")).toEqual({
+      key1: "",
+      key2: "value2",
+    });
+  });
+
+  test("parses value with special characters", () => {
+    expect(parseQueryString("greeting=Hello%2C+World%21")).toEqual({
+      greeting: "Hello%2C+World%21",
+    });
   });
 });

Sprint-2/implement/tally.js

@@ -1,3 +1,13 @@
-function tally() {}
+function tally(arr) {
+  if (!Array.isArray(arr)) {
+    throw new Error("Input must be an array");
+  }
+
+  const counts = {};
+  for (const item of arr) {
+    counts[item] = (counts[item] || 0) + 1;
+  }
+  return counts;
+}
 
 module.exports = tally;

Sprint-2/implement/tally.test.js

@@ -16,19 +16,33 @@ const tally = require("./tally.js");
 
 // Acceptance criteria:
 
-// Given a function called tally
-// When passed an array of items
-// Then it should return an object containing the count for each unique item
+describe("tally", () => {
+  // Given a function called tally
+  // When passed an array of items
+  // Then it should return an object containing the count for each unique item
 
-// 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 empty array
+  // When passed to tally
+  // Then it should return 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
+  // 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", "g", "b", "a", "b", "a"])).toEqual({
+      a: 4,
+      b: 2,
+      g: 1,
+    });
+  });
 
-// Given an invalid input like a string
-// When passed to tally
-// Then it should throw an error
+  // 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", () => {
+    expect(() => tally({})).toThrow("Input must be an array");
+  });
+});

Sprint-2/interpret/invert.js

@@ -10,20 +10,28 @@ function invert(obj) {
   const invertedObj = {};
 
   for (const [key, value] of Object.entries(obj)) {
-    invertedObj.key = value;
+    invertedObj[value] = key;
   }
 
   return invertedObj;
 }
+module.exports = invert;
 
 // a) What is the current return value when invert is called with { a : 1 }
+// I think its { key: 1 }
 
 // b) What is the current return value when invert is called with { a: 1, b: 2 }
+// I think it should be { key: 2 }
 
 // c) What is the target return value when invert is called with {a : 1, b: 2}
+// my suggestion is { '1': 'a', '2': 'b' }
 
 // c) What does Object.entries return? Why is it needed in this program?
+// Object.entries returns an array of a given object's own enumerable string-keyed property [key, value] pairs.
+// It is needed in this program to iterate over the key-value pairs of the object to swap them.
 
 // d) Explain why the current return value is different from the target output
+// I think its different because in the line invertedObj.key = value;
+// the key is being set as the string "key" instead of using the variable key.
 
 // e) Fix the implementation of invert (and write tests to prove it's fixed!)

Sprint-2/interpret/invert.test.js

@@ -0,0 +1,38 @@
+const invert = require("./invert.js");
+
+describe("invert", () => {
+  // Given an object with one key-value pair
+  // When invert is called with this object
+  // Then it should return an object with the key and value swapped
+  test("invert swaps key and value for single pair", () => {
+    expect(invert({ a: 1 })).toEqual({ 1: "a" });
+  });
+
+  // Given an object with multiple key-value pairs
+  // When invert is called with this object
+  // Then it should return an object with the keys and values swapped
+  test("invert swaps keys and values for multiple pairs", () => {
+    expect(invert({ a: 1, b: 2 })).toEqual({ 1: "a", 2: "b" });
+  });
+
+  // Given an object with string values
+  // When invert is called with this object
+  // Then it should return an object with the keys and values swapped
+  test("invert swaps keys and values for string values", () => {
+    expect(invert({ x: "apple", y: "banana" })).toEqual({
+      apple: "x",
+      banana: "y",
+    });
+  });
+
+  // Given an object with mixed value types
+  // When invert is called with this object
+  // Then it should return an object with the keys and values swapped
+  test("invert swaps keys and values for mixed value types", () => {
+    expect(invert({ a: 1, b: "two", c: 3 })).toEqual({
+      1: "a",
+      two: "b",
+      3: "c",
+    });
+  });
+});