Manchester | 26-ITP-Jan | Khalidbih | Sprint 2 | Data Groups

Sprint-2/debug/address.js

@@ -1,5 +1,7 @@
 // Predict and explain first...
-
+// this code will throw an error. because the text `My house number is ${address[0]}` is not inside backticks.
+// so JavaScript doesn’t see it as a string.
+// Instead, it thinks `My` is a variable name, but that variable doesn’t exist.
 // This code should log out the houseNumber from the address object
 // but it isn't working...
 // Fix anything that 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

@@ -1,5 +1,7 @@
 // Predict and explain first...
-
+// This code will throw an error.`author` is an object.
+// and `for…of` only works on arrays or strings.
+// Use `Object.values(author)` or `for…in` to loop over object values.
 // 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

@@ -1,5 +1,6 @@
 // Predict and explain first...
-
+// `recipe` is an object. `${recipe}` prints [object Object], not the ingredients.
+// To log ingredients, loop over `recipe.ingredients` or join them into a string.
 // 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?
@@ -11,5 +12,5 @@ const recipe = {
 };
 
 console.log(`${recipe.title} serves ${recipe.serves}
-  ingredients:
-${recipe}`);
+ingredients:
+${recipe.ingredients.join("\n")}`);

Sprint-2/implement/contains.js

@@ -1,3 +1,8 @@
-function contains() {}
+function contains(obj, key) {
+  if (obj === null || typeof obj !== "object" || Array.isArray(obj)) {
+    return false;
+  }
+  return Object.hasOwn(obj, key);
+}
 
 module.exports = contains;

Sprint-2/implement/contains.test.js

@@ -20,16 +20,28 @@ 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");
+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 for invalid input like an array", () => {
+  expect(contains([1, 2, 3], "0")).toBe(false);
+  expect(contains(null, "a")).toBe(false);
+  expect(contains("string", "0")).toBe(false);
+});

Sprint-2/implement/lookup.js

@@ -1,5 +1,11 @@
-function createLookup() {
-  // implementation here
+function createLookup(pairs) {
+  const result = {};
+
+  for (const [key, value] of pairs) {
+    result[key] = value;
+  }
+
+  return result;
 }
 
 module.exports = createLookup;

Sprint-2/implement/lookup.test.js

@@ -1,6 +1,18 @@
 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"],
+  ];
+
+  expect(createLookup(countryCurrencyPairs)).toEqual({
+    US: "USD",
+    CA: "CAD",
+    GB: "GBP",
+  });
+});
 
 /*
 

Sprint-2/implement/querystring.js

@@ -1,13 +1,35 @@
 function parseQueryString(queryString) {
   const queryParams = {};
+
+  if (queryString.startsWith("?")) {
+    queryString = queryString.slice(1);
+  }
+
   if (queryString.length === 0) {
     return queryParams;
   }
-  const keyValuePairs = queryString.split("&");
 
-  for (const pair of keyValuePairs) {
-    const [key, value] = pair.split("=");
-    queryParams[key] = value;
+  const pairs = queryString.split("&");
+
+  for (const pair of pairs) {
+    const index = pair.indexOf("=");
+    let key, value;
+
+    if (index === -1) {
+      key = pair;
+      value = undefined;
+    } else {
+      key = pair.slice(0, index);
+      value = pair.slice(index + 1);
+    }
+
+    const decodedKey = decodeURIComponent(key);
+
+    if (value === undefined || value === "") {
+      queryParams[decodedKey] = undefined;
+    } else {
+      queryParams[decodedKey] = decodeURIComponent(value);
+    }
   }
 
   return queryParams;

Sprint-2/implement/querystring.test.js

@@ -3,10 +3,24 @@
 // 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",
+    equation: "x=y+1",
+  });
+});
+
+test("handles keys with empty values as undefined", () => {
+  expect(parseQueryString("key1=&key2=value2")).toEqual({
+    key1: undefined,
+    key2: "value2",
+  });
+});
+
+test("handles keys without = as undefined", () => {
+  expect(parseQueryString("key1&key2=value2")).toEqual({
+    key1: undefined,
+    key2: "value2",
   });
 });

Sprint-2/implement/tally.js

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

Sprint-2/implement/tally.test.js

@@ -19,16 +19,30 @@ const tally = require("./tally.js");
 // Given a function called tally
 // When passed an array of items
 // Then it should return an object containing the count for each unique item
+test("counts single item correctly", () => {
+  expect(tally(["a"])).toEqual({ a: 1 });
+});
 
 // 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("returns empty object for empty array", () => {
+  expect(tally([])).toEqual({});
+});
 
 // Given an array with duplicate items
 // When passed to tally
 // Then it should return counts for each unique item
 
+test("counts each unique item correctly", () => {
+  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 error if input is not an array", () => {
+  expect(() => tally("not an array")).toThrow("Input must be an array");
+  expect(() => tally(123)).toThrow("Input must be an array");
+  expect(() => tally({})).toThrow("Input must be an array");
+});

Sprint-2/interpret/invert.js

@@ -10,20 +10,34 @@ 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 }
+// { "1": "a" }
 
 // b) What is the current return value when invert is called with { a: 1, b: 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?
+// Returns an array of [key, value] pairs. It lets us loop over keys and values easily.
 
 // d) Explain why the current return value is different from the target output
+// The original function used "key" literally, so the object’s keys weren’t swapped correctly.
+// The fixed version uses `invertedObj[value] = key` to swap keys and values.
 
 // e) Fix the implementation of invert (and write tests to prove it's fixed!)
+
+const invert = require("./invert.js");
+
+test("inverts single key-value object", () => {
+  expect(invert({ a: 1 })).toEqual({ 1: "a" });
+});
+
+test("inverts multiple key-value pairs", () => {
+  expect(invert({ a: 1, b: 2 })).toEqual({ 1: "a", 2: "b" });
+});