London | May-2025| Anuar Duisenbek | Module-Data -Groups | Sprint-2

Sprint-2/debug/address.js

@@ -12,4 +12,4 @@ 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

@@ -11,6 +11,6 @@ const author = {
   alive: true,
 };
 
-for (const value of author) {
+for (const value of Object.values(author)) {
   console.log(value);
 }

Sprint-2/debug/recipe.js

@@ -12,4 +12,4 @@ const recipe = {
 
 console.log(`${recipe.title} serves ${recipe.serves}
   ingredients:
-${recipe}`);
+${recipe.ingredients.join("\n")}`);

Sprint-2/implement/contains.js

@@ -1,3 +1,8 @@
-function contains() {}
+function contains(obj, prop) {
+  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 +20,27 @@ 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 returns false for 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("contains returns true for an 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 a 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 array input", () => {
+  expect(contains([1, 2, 3], "a")).toBe(false);
+});

Sprint-2/implement/lookup.js

@@ -1,5 +1,9 @@
-function createLookup() {
-  // implementation here
+function createLookup(countryCurrencyPairs) {
+  let lookup = {};
+  for (let [country, currency] of countryCurrencyPairs) {
+    lookup[country] = currency;
+  }
+  return lookup;
 }
 
 module.exports = createLookup;

Sprint-2/implement/lookup.test.js

@@ -1,7 +1,20 @@
 const createLookup = require("./lookup.js");
 
-test.todo("creates a country currency code lookup for multiple codes");
-
+test("returns an empty object for an empty input array", () => {
+  expect(createLookup([])).toEqual({});
+});
+
+test("creates a country currency code lookup for multiple codes", () => {
+  const countryCurrencyPairs = [
+    ["US", "USD"],
+    ["CA", "CAD"],
+  ];
+  const output = {
+    US: "USD",
+    CA: "CAD",
+  };
+  expect(createLookup(countryCurrencyPairs)).toEqual(output);
+});
 /*
 
 Create a lookup object of key value pairs from an array of code pairs

Sprint-2/implement/querystring.js

@@ -6,7 +6,15 @@ function parseQueryString(queryString) {
   const keyValuePairs = queryString.split("&");
 
   for (const pair of keyValuePairs) {
-    const [key, value] = pair.split("=");
+    const idx = pair.indexOf("=");
+    let key, value;
+    if (idx === -1) {
+      key = decodeURIComponent(pair);
+      value = undefined;
+    } else {
+      key = decodeURIComponent(pair.slice(0, idx));
+      value = decodeURIComponent(pair.slice(idx + 1));
+    }
     queryParams[key] = value;
   }
 

Sprint-2/implement/querystring.test.js

@@ -3,10 +3,22 @@
 // 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 empty string", () => {
+  expect(parseQueryString("")).toEqual({});
+});
+
+test("parses key with empty value", () => {
+  expect(parseQueryString("abc=")).toEqual({ abc: "" });
+});
 
 test("parses querystring values containing =", () => {
-  expect(parseQueryString("equation=x=y+1")).toEqual({
-    "equation": "x=y+1",
+  expect(parseQueryString("ab=x=y+1")).toEqual({
+    ab: "x=y+1",
   });
 });
+
+test("parses multiple pairs", () => {
+  expect(parseQueryString("a=1&b=2")).toEqual({ a: "1", b: "2" });
+});

Sprint-2/implement/tally.js

@@ -1,3 +1,19 @@
-function tally() {}
+function tally(arr) {
+  if (!Array.isArray(arr)) {
+    throw new Error("Input should be an array");
+  }
+  const obj = {};
+  if (arr.length === 0) {
+    return obj;
+  }
+  arr.forEach((item) => {
+    if (obj[item]) {
+      obj[item]++;
+    } else {
+      obj[item] = 1;
+    }
+  });
+  return obj;
+}
 
 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("tally returns empty object for empty array", () => {
+  expect(
+    tally(["apple", "banana", "apple", "orange", "banana", "apple"])
+  ).toEqual({ apple: 3, banana: 2, orange: 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("tally 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("tally counts repeated elements", () => {
+  expect(tally(["a", ["a"]])).toEqual({ a: 2 });
+  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("Given an invalid input like a string, throw an error", () => {
+  expect(() => tally("abc")).toThrow("Input should be an array");
+});

Sprint-2/interpret/invert.js

@@ -7,23 +7,39 @@
 // E.g. invert({x : 10, y : 20}), target output: {"10": "x", "20": "y"}
 
 function invert(obj) {
+  if (obj.length === 0) {
+    return 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 }
+// invert({ a: 1 });
 
 // b) What is the current return value when invert is called with { a: 1, b: 2 }
+// invert({ 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?
+/*
+Using Object.entries() allows you to use a for...of loop 
+ to access both keys making it easy to swap them when creating a new object.
+ */
 
 // d) Explain why the current return value is different from the target output
 
+//Because in the line 13 the invertedObj.key statement
+// is not using the value of the key variable.
+
 // e) Fix the implementation of invert (and write tests to prove it's fixed!)

Sprint-2/interpret/invert.test.js

@@ -0,0 +1,20 @@
+const invert = require("./invert");
+
+test("handles empty object", () => {
+  expect(invert({})).toEqual({});
+});
+
+test("invert returns empty object for empty obj", () => {
+  expect(invert({ x: 10, y: 20 })).toEqual({ 10: "x", 20: "y" });
+});
+
+test("inverts an object with numbers as values", () => {
+  expect(invert({ a: 1, b: 2 })).toEqual({ 1: "a", 2: "b" });
+});
+
+test("inverts an object with string values", () => {
+  expect(invert({ cat: "animal", carrot: "vegetable" })).toEqual({
+    animal: "cat",
+    vegetable: "carrot",
+  });
+});