London | ITP-JAN26 | Ihor Taradaiko | Sprint 2 | Coursework/sprint-2

Sprint-2/debug/address.js

@@ -1,5 +1,11 @@
 // Predict and explain first...
 
+// This will log "My house number is undefined" because
+// address[0] is looking for index 0 like it's an array, but address
+// is an object. To get a value from an object you need to use the
+// key name, not a number. Changing address[0] to address.houseNumber
+// will fix it and log "My house number is 42".
+
 // This code should log out the houseNumber from the address object
 // but it isn't working...
 // Fix anything that isn't working
@@ -12,4 +18,4 @@ 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...
+// This code will throw a TypeError: "author is not iterable".
+//
 
 // 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

@@ -1,15 +1,23 @@
 // Predict and explain first...
+// This will not log the ingredients correctly. It will print the whole
+// recipe object as [object Object] instead of each ingredient on its own line,
+// because you're interpolating the entire object (`${recipe}`) instead of
+// its properties and the ingredients array items.
 
 // 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?
 
+
 const recipe = {
   title: "bruschetta",
   serves: 2,
   ingredients: ["olive oil", "tomatoes", "salt", "pepper"],
 };
 
 console.log(`${recipe.title} serves ${recipe.serves}
-  ingredients:
-${recipe}`);
+ingredients:`);
+
+for (const ingredient of recipe.ingredients) {
+  console.log(ingredient);
+}

Sprint-2/implement/contains.js

@@ -1,3 +1,11 @@
-function contains() {}
+function contains(obj, propName) {
+  // Return false for non-objects or null
+  if (obj === null || typeof obj !== "object" || Array.isArray(obj)) {
+    return false;
+  }
+
+  // Check if the object has the property as its own key
+  return Object.hasOwn(obj, propName);
+}
 
 module.exports = contains;

Sprint-2/implement/contains.test.js

@@ -1,35 +1,57 @@
 const contains = require("./contains.js");
 
+
 /*
 Implement a function called contains that checks an object contains a
 particular property
 
+
 E.g. contains({a: 1, b: 2}, 'a') // returns true
 as the object contains a key of 'a'
 
+
 E.g. contains({a: 1, b: 2}, 'c') // returns false
 as the object doesn't contains a key of 'c'
 */
 
+
 // Acceptance criteria:
 
+
 // Given a contains function
 // 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");
+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 returns true for existing property", () => {
+  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("contains returns false for non-existent property", () => {
+  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("contains returns false when first argument is an array even if key exists", () => {
+  const arr = ["a", "b", "c"]; 
+
+  expect(contains(arr, "0")).toBe(false);
+});

Sprint-2/implement/lookup.js

@@ -1,5 +1,12 @@
-function createLookup() {
+function createLookup(countryCurrencyPairs) {
   // implementation here
+  const lookup = {};
+
+  for (const [countryCode, currencyCode] of countryCurrencyPairs) {
+    lookup[countryCode] = currencyCode;
+  }
+
+  return lookup;
 }
 
 module.exports = createLookup;

Sprint-2/implement/lookup.test.js

@@ -1,31 +1,54 @@
 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", () => {
+  const countryCurrencyPairs = [
+    ["US", "USD"],
+    ["CA", "CAD"],
+    ["GB", "GBP"],
+  ];
+
+  const result = createLookup(countryCurrencyPairs);
+
+  expect(result).toEqual({
+    US: "USD",
+    CA: "CAD",
+    GB: "GBP",
+  });
+});
+
 
 /*
 
+
 Create a lookup object of key value pairs from an array of code pairs
 
+
 Acceptance Criteria:
 
+
 Given
  - An array of arrays representing country code and currency code pairs
    e.g. [['US', 'USD'], ['CA', 'CAD']]
 
+
 When
  - createLookup function is called with the country-currency array as an argument
 
+
 Then
  - It should return an object where:
  - The keys are the country codes
  - The values are the corresponding currency codes
 
+
 Example
 Given: [['US', 'USD'], ['CA', 'CAD']]
 
+
 When
 createLookup(countryCurrencyPairs) is called
 
+
 Then
 It should return:
  {

Sprint-2/implement/querystring.js

@@ -3,14 +3,32 @@ function parseQueryString(queryString) {
   if (queryString.length === 0) {
     return queryParams;
   }
+
   const keyValuePairs = queryString.split("&");
 
   for (const pair of keyValuePairs) {
-    const [key, value] = pair.split("=");
+    if (pair === "") {
+      continue;
+    }
+
+    const indexOfEquals = pair.indexOf("=");
+    let key;
+    let value;
+
+    if (indexOfEquals === -1) {
+      // no "=", treat whole pair as key with empty value
+      key = pair;
+      value = "";
+    } else {
+      key = pair.slice(0, indexOfEquals);
+      value = pair.slice(indexOfEquals + 1);
+    }
+
     queryParams[key] = value;
   }
 
   return queryParams;
 }
 
+
 module.exports = parseQueryString;

Sprint-2/implement/querystring.test.js

@@ -3,10 +3,34 @@
 // 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")
 
+
 test("parses querystring values containing =", () => {
   expect(parseQueryString("equation=x=y+1")).toEqual({
     "equation": "x=y+1",
   });
 });
+
+test("parses empty querystring as empty object", () => {
+  expect(parseQueryString("")).toEqual({});
+});
+
+test("parses single key with empty value", () => {
+  expect(parseQueryString("flag=")).toEqual({ flag: "" });
+});
+
+test("parses key with no =", () => {
+  expect(parseQueryString("flag")).toEqual({ flag: "" });
+});
+
+test("parses multiple key value pairs", () => {
+  expect(parseQueryString("a=1&b=2")).toEqual({ a: "1", b: "2" });
+});
+
+test("later duplicate keys overwrite earlier ones", () => {
+  expect(parseQueryString("a=1&a=2")).toEqual({ a: "2" });
+});
+
+

Sprint-2/implement/tally.js

@@ -1,3 +1,15 @@
-function tally() {}
+function tally(items) {
+  if (!Array.isArray(items)) {
+    throw new Error("tally expects an array");
+  }
 
-module.exports = tally;
+  const counts = Object.create(null);
+
+  for (const item of items) {
+    counts[item] = (counts[item] || 0) + 1;
+  }
+
+  return counts;
+}
+
+module.exports = tally;

Sprint-2/implement/tally.test.js

@@ -1,5 +1,6 @@
 const tally = require("./tally.js");
 
+
 /**
  * tally array
  *
@@ -14,21 +15,39 @@ const tally = require("./tally.js");
  * tally(['a', 'a', 'b', 'c']), target output: { a : 2, b: 1, c: 1 }
  */
 
+
 // 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
 
+
 // 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 counts each unique item", () => {
+  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("tally throws on invalid input", () => {
+  expect(() => tally("not an array")).toThrow();
+});
+
+
+

Sprint-2/interpret/invert.js

@@ -1,29 +1,49 @@
 // Let's define how invert should work
 
+
 // Given an object
 // When invert is passed this object
 // 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 = {};
 
   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 }
+// Answer: { key: 1 }
+
 
 // b) What is the current return value when invert is called with { a: 1, b: 2 }
+// Answer: { key: 2 }
+
 
 // c) What is the target return value when invert is called with {a : 1, b: 2}
+// Answer: { "1": "a", "2": "b" }
+
 
 // c) What does Object.entries return? Why is it needed in this program?
+// Answer: Object.entries(obj) returns an array of [key, value] pairs,
+// It is needed so we can loop over the object and easily get both key and value in the for...of loop using array destructuring: [key, value].
+
 
 // d) Explain why the current return value is different from the target output
+// Answer: In this implementation, the current return value already matches the target output, because we correctly use the value as the new key
+// and the key as the new value: invertedObj[value] = key.
+
 
 // e) Fix the implementation of invert (and write tests to prove it's fixed!)
+// Answer: No changes needed to the implementation; it already works as required.
+