London | 26-ITP-Jan | Xuanming Hu | Sprint 2 | Data Groups

Sprint-2/debug/address.js

@@ -1,5 +1,5 @@
 // Predict and explain first...
-
+// Prediction: 'address' is an object, not an array. Trying to access it with [0] will return undefined.
 // This code should log out the houseNumber from the address object
 // but it isn't working...
 // Fix anything that isn't working
@@ -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

@@ -1,5 +1,5 @@
 // Predict and explain first...
-
+// Prediction: 'author' is an object, not an array. The 'for...of' loop doesn't work on plain objects, so it will throw an error.
 // 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 +11,6 @@ const author = {
   alive: true,
 };
 
-for (const value of author) {
-  console.log(value);
+for (const key in author) {
+  console.log(author[key]);
 }

Sprint-2/debug/recipe.js

@@ -1,5 +1,5 @@
 // Predict and explain first...
-
+// Prediction: The code is trying to print the whole 'recipe' object directly in the template literal, which will just output "[object Object]". We need to access its properties.
 // 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 +11,5 @@ 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(object, propertyName) {
+  if (typeof object !== "object" || object === null || Array.isArray(object)) {
+    return false;
+  }
+  return object.hasOwnProperty(propertyName);
+}
 
 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 on empty object returns false", () => {
+  expect(contains({}, "a")).toEqual(false);
+});
 
 // Given an object with properties
 // When passed to contains with an existing property name
 // Then it should return true
-
+test("contains with an existing property name returns true", () => {
+  expect(contains({ a: 1, b: 2 }, "a")).toEqual(true);
+});
 // Given an object with properties
 // When passed to contains with a non-existent property name
 // Then it should return false
-
+test("contains with a non-existent property name returns false", () => {
+  expect(contains({ a: 1, b: 2 }, "c")).toEqual(false);
+});
 // Given invalid parameters like an array
 // When passed to contains
 // Then it should return false or throw an error
+test("contains with invalid parameters like an array or null returns false", () => {
+  expect(contains([1, 2, 3], "0")).toEqual(false);
+  expect(contains(null, "a")).toEqual(false);
+  expect(contains("not an object", "length")).toEqual(false);
+});

Sprint-2/implement/lookup.js

@@ -1,5 +1,15 @@
-function createLookup() {
-  // implementation here
+function createLookup(countryCurrencyPairs) {
+  if (!Array.isArray(countryCurrencyPairs)) {
+    return {};
+  }
+
+  const lookupObject = {};
+
+  for (const [country, currency] of countryCurrencyPairs) {
+    lookupObject[country] = currency;
+  }
+
+  return lookupObject;
 }
 
 module.exports = createLookup;

Sprint-2/implement/lookup.test.js

@@ -1,6 +1,22 @@
 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"],
+  ];
+
+  const expectedOutput = {
+    US: "USD",
+    CA: "CAD",
+  };
+
+  expect(createLookup(countryCurrencyPairs)).toEqual(expectedOutput);
+});
+
+test("returns an empty object if an empty array is passed", () => {
+  expect(createLookup([])).toEqual({});
+});
 
 /*
 

Sprint-2/implement/querystring.js

@@ -6,7 +6,9 @@ function parseQueryString(queryString) {
   const keyValuePairs = queryString.split("&");
 
   for (const pair of keyValuePairs) {
-    const [key, value] = pair.split("=");
+    if (!pair) continue;
+    const [key, ...rest] = pair.split("=");
+    const value = rest.join("=");
     queryParams[key] = value;
   }
 

Sprint-2/implement/querystring.test.js

@@ -3,10 +3,28 @@
 // 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("returns an empty object when query string is empty", () => {
+  expect(parseQueryString("")).toEqual({});
+});
+
+test("handles keys without values properly", () => {
+  expect(parseQueryString("foo&bar=2")).toEqual({
+    foo: "",
+    bar: "2",
+  });
+});
+
+test("handles consecutive ampersands (empty pairs) correctly", () => {
+  expect(parseQueryString("key1=value1&&key2=value2")).toEqual({
+    key1: "value1",
+    key2: "value2",
   });
 });

Sprint-2/implement/tally.js

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

Sprint-2/implement/tally.test.js

@@ -23,12 +23,34 @@ 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("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 returns counts for each unique item", () => {
+  const input = ["a", "a", "b", "c"];
+  const expectedOutput = { a: 2, b: 1, c: 1 };
+  expect(tally(input)).toEqual(expectedOutput);
+});
 // Given an invalid input like a string
 // When passed to tally
 // Then it should throw an error
+test("throws an error when input is not an array", () => {
+  expect(() => {
+    tally("not an array");
+  }).toThrow("Input must be an array");
+
+  expect(() => {
+    tally(null);
+  }).toThrow();
+});
+
+test("handles built-in property names like toString correctly", () => {
+  const result = tally(["toString", "toString"]);
+  const expected = Object.create(null);
+  expected.toString = 2;
+  expect(result).toEqual(expected);
+});

Sprint-2/interpret/invert.js

@@ -10,20 +10,22 @@ 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?
-
+// It returns an array of a given object's own enumerable string-keyed property [key, value] pairs.
+// It is needed because plain JavaScript objects are not iterable by default, so we cannot use a 'for...of' loop directly on an object without it.
 // d) Explain why the current return value is different from the target output
-
+// Using dot notation (invertedObj.key) creates a literal property named "key" instead of evaluating the variable.
+// We must use bracket notation (invertedObj[value]) to dynamically set the property name using the variable's value.
 // e) Fix the implementation of invert (and write tests to prove it's fixed!)

Sprint-2/interpret/invert.test.js

@@ -0,0 +1,23 @@
+const invert = require("./invert");
+
+describe("invert function", () => {
+  test("swaps keys and values for an object with numeric values", () => {
+    expect(invert({ a: 1, b: 2 })).toEqual({ 1: "a", 2: "b" });
+  });
+
+  test("swaps keys and values for a single pair object", () => {
+    expect(invert({ x: 99 })).toEqual({ 99: "x" });
+  });
+
+  test("returns an empty object when passed an empty object", () => {
+    expect(invert({})).toEqual({});
+  });
+
+  test("handles string values correctly", () => {
+    expect(invert({ 1: "one", 2: "two" })).toEqual({ one: "1", two: "2" });
+  });
+
+  test("handles mixed type values correctly", () => {
+    expect(invert({ a: 1, b: "hello" })).toEqual({ 1: "a", hello: "b" });
+  });
+});