London | May-2026-itp | Vitalii Kmit | Sprint 2 | Data Groups exercises

Sprint-2/debug/address.js

@@ -1,4 +1,6 @@
 // Predict and explain first...
+// I think that it will not run because we're trying to access an object on line 15
+// Instead it should be ${adddress[houseNumber]}
 
 // This code should log out the houseNumber from the address object
 // but it isn't working...
@@ -12,4 +14,4 @@ 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...
+// Because it's trying to iterate through an object
+// It should just print author without a loop
 
 // 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 +13,4 @@ const author = {
   alive: true,
 };
 
-for (const value of author) {
-  console.log(value);
-}
+console.log(Object.values(author));

Sprint-2/debug/recipe.js

@@ -1,4 +1,6 @@
 // Predict and explain first...
+// I think it should use recipe.ingredients instead of recipe at line 15
+// Ok I tried it and now I think that it should be done with a loop to list the ingredients
 
 // This program should log out the title, how many it serves and the ingredients.
 // Each ingredient should be logged on a new line
@@ -11,5 +13,8 @@ const recipe = {
 };
 
 console.log(`${recipe.title} serves ${recipe.serves}
-  ingredients:
-${recipe}`);
+ingredients:`);
+
+for (const i of recipe.ingredients) {
+  console.log(i);
+}

Sprint-2/implement/contains.js

@@ -1,3 +1,21 @@
-function contains() {}
+function contains(toCheck, input) {
+  if (
+    typeof toCheck !== "object" ||
+    Array.isArray(toCheck) ||
+    toCheck === null
+  ) {
+    return false;
+  }
+
+  for (const key in toCheck) {
+    if (key === input) {
+      return true;
+    }
+  }
+
+  return false;
+}
+
+console.log(contains({ a: 1, b: 2 }, "a"));
 
 module.exports = contains;

Sprint-2/implement/contains.test.js

@@ -17,10 +17,17 @@ 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
 
+test(`Should return true if object contains the property`, () => {
+  expect(contains({ a: 1, b: 2 }, "a")).toEqual(true);
+  expect(contains({ b: 2 }, "a")).toEqual(false);
+});
+
 // Given an empty object
 // When passed to contains
 // Then it should return false
-test.todo("contains on empty object returns false");
+test(`Should return false if object is empty`, () => {
+  expect(contains({}, "a")).toEqual(false);
+});
 
 // Given an object with properties
 // When passed to contains with an existing property name
@@ -33,3 +40,7 @@ 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
+
+test(`Should return false if given wron type`, () => {
+  expect(contains(["a", "b"], "0")).toEqual(false);
+});

Sprint-2/implement/lookup.js

@@ -1,5 +1,22 @@
-function createLookup() {
+function createLookup(array) {
   // implementation here
+
+  if (!Array.isArray(array)) {
+    throw new Error("Wrong input type, expected array");
+  }
+
+  if (array.length === 0) {
+    throw new Error("Array is empty");
+  }
+
+  let output = {};
+  for (const pair of array) {
+    const key = pair[0];
+    const value = pair[1];
+
+    output[key] = value;
+  }
+  return output;
 }
 
 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 +31,18 @@ It should return:
    'CA': 'CAD'
  }
 */
+
+test(`Should return an object with correct keys`, () => {
+  expect(
+    createLookup([
+      ["US", "USD"],
+      ["CA", "CAD"],
+    ])
+  ).toEqual({ US: "USD", CA: "CAD" });
+});
+
+test(`Should throw an error if no input given`, () => {
+  expect(() => {
+    createLookup();
+  }).toThrow();
+});

Sprint-2/implement/querystring.js

@@ -1,13 +1,35 @@
 function parseQueryString(queryString) {
   const queryParams = {};
+
+  // return if input is 0
   if (queryString.length === 0) {
     return queryParams;
   }
+
+  // replace all + by ' '
+  queryString = queryString.replaceAll("+", " ");
+
+  // split by &
   const keyValuePairs = queryString.split("&");
 
   for (const pair of keyValuePairs) {
-    const [key, value] = pair.split("=");
-    queryParams[key] = value;
+    if (pair.length > 0) {
+      const parts = pair.split("=");
+      // first part as the key
+      const key = decodeURIComponent(parts[0]);
+      // second to last parts as the value
+      const value = decodeURIComponent(parts.slice(1).join("="));
+
+      // if no key then assign new value
+      if (!Object.hasOwn(queryParams, key)) {
+        queryParams[key] = value;
+      } else if (Array.isArray(queryParams[key])) {
+        queryParams[key].push(value);
+        // if not array then turn into array with old and new values
+      } else {
+        queryParams[key] = [queryParams[key], value];
+      }
+    }
   }
 
   return queryParams;

Sprint-2/implement/tally.js

@@ -1,3 +1,23 @@
-function tally() {}
+function tally(input) {
+  let out = {};
+
+  if (!Array.isArray(input)) {
+    throw new Error(
+      `Wrong input type, expected an array but got ${typeof input}`
+    );
+  }
+
+  for (const i of input) {
+    if (!Object.hasOwn(out, i)) {
+      out[i] = 1;
+    } else {
+      out[i] = out[i] + 1;
+    }
+  }
+
+  return out;
+}
+
+console.log(tally(["a", "a", "b"]));
 
 module.exports = tally;

Sprint-2/implement/tally.test.js

@@ -23,12 +23,23 @@ 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(`Should an empty object when empty array is passed`, () => {
+  expect(tally([])).toEqual({});
+});
 
 // Given an array with duplicate items
 // When passed to tally
 // Then it should return counts for each unique item
+test(`Should return counts for each unique item`, () => {
+  expect(tally(["a", "a", "b"])).toEqual({ a: 2, b: 1 });
+  expect(tally(["toString", "a", "b"])).toEqual({ toString: 1, a: 1, b: 1 });
+});
 
 // Given an invalid input like a string
 // When passed to tally
 // Then it should throw an error
+test(`Should return an error when given wrong input type`, () => {
+  expect(() => {
+    tally("hello");
+  }).toThrow();
+});

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 }
+// { 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}
+// { 1 : a, 2 : b }
 
 // c) What does Object.entries return? Why is it needed in this program?
+// Object.entries(obj) returns an array of [key, value] pairs, one small array for each property in the object
 
 // d) Explain why the current return value is different from the target output
+// because the key and value wasn't inverted in the code
 
 // e) Fix the implementation of invert (and write tests to prove it's fixed!)
+// ok!

Sprint-2/interpret/invert.test.js

@@ -0,0 +1,30 @@
+const invert = require("./invert.js");
+
+describe("invert", () => {
+  test("should swap keys and values for a simple object", () => {
+    expect(invert({ x: 10, y: 20 })).toEqual({ 10: "x", 20: "y" });
+  });
+
+  test("should work with a single key-value pair", () => {
+    expect(invert({ a: 1 })).toEqual({ 1: "a" });
+  });
+
+  test("should return an empty object when given an empty object", () => {
+    expect(invert({})).toEqual({});
+  });
+
+  test("should overwrite earlier keys when two values are the same", () => {
+    // if two keys share the same value, the later key wins after inversion
+    expect(invert({ a: 1, b: 1 })).toEqual({ 1: "b" });
+  });
+
+  test("should coerce numeric and boolean values to string keys", () => {
+    expect(invert({ a: true, b: false })).toEqual({ true: "a", false: "b" });
+  });
+
+  test("should not mutate the original object", () => {
+    const original = { a: 1, b: 2 };
+    invert(original);
+    expect(original).toEqual({ a: 1, b: 2 });
+  });
+});