London | 25-ITP-September | Ammad Ur Rehman | Sprint 3 | [TECH ED] Complete sprint 2 exercises

Sprint-2/debug/address.js

@@ -1,5 +1,8 @@
 // Predict and explain first...
 
+// I predict that the console will log "My house number is undefined"
+// because it is using array index notation whereas address is an object.
+
 // This code should log out the houseNumber from the address object
 // but it isn't working...
 // Fix anything that isn't working
@@ -12,4 +15,4 @@ 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

@@ -1,8 +1,14 @@
 // Predict and explain first...
 
+// I predict that the console will log "undefined" because
+// it is looping through elements in a collection (e.g. arrays and sets)
+// whereas author is an object.
+
 // 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
 
+// The loop is trying to loop through an array
+
 const author = {
   firstName: "Zadie",
   lastName: "Smith",
@@ -11,6 +17,6 @@ const author = {
   alive: true,
 };
 
-for (const value of author) {
+for (value in author) {
   console.log(value);
 }

Sprint-2/debug/recipe.js

@@ -1,5 +1,7 @@
 // Predict and explain first...
 
+// The console will print the recipe title, serves and the recipe object itself rather than the actual ingredient
+
 // 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?
@@ -10,6 +12,8 @@ const recipe = {
   ingredients: ["olive oil", "tomatoes", "salt", "pepper"],
 };
 
-console.log(`${recipe.title} serves ${recipe.serves}
-  ingredients:
-${recipe}`);
+console.log(
+  `titie: ${recipe.title}, serves: ${
+    recipe.serves
+  }, ingredients: ${recipe.ingredients.join(", ")}`
+);

Sprint-2/implement/contains.js

@@ -1,3 +1,9 @@
-function contains() {}
+function contains(object, property) {
+  if (object === null || typeof object !== "object" || Array.isArray(object)) {
+    throw new Error("object is not an object type!");
+  }
+
+  return Object.prototype.hasOwnProperty.call(object, property);
+}
 
 module.exports = contains;

Sprint-2/implement/contains.test.js

@@ -16,20 +16,44 @@ as the object doesn't contains a key of 'c'
 // 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
+test("object contains the property returns true", () => {
+  const object = { forename: "John" };
+  expect(contains(object, "forename")).toEqual(true);
+  expect(contains(object, "surname")).toEqual(false);
+});
 
 // Given an empty object
 // When passed to contains
 // Then it should return false
-test.todo("contains on empty object returns false");
+test("empty object returns false", () => {
+  const object = {};
+  const result = contains(object);
+  expect(result).toEqual(false);
+});
 
 // Given an object with properties
 // When passed to contains with an existing property name
 // Then it should return true
+test("object contains properties returns true for a property", () => {
+  const object = { forename: "John", surname: "Appleseed" };
+  const property = "surname";
+  const result = contains(object, property);
+  expect(result).toEqual(true);
+});
 
 // Given an object with properties
 // When passed to contains with a non-existent property name
 // Then it should return false
+test("object returns false for a non-existent property", () => {
+  const object = { forename: "John", surname: "Appleseed" };
+  const property = "middlename";
+  const result = contains(object, property);
+  expect(result).toEqual(false);
+});
 
 // Given invalid parameters like an array
 // When passed to contains
 // Then it should return false or throw an error
+test("object throws an error for a non-object type", () => {
+  expect(() => contains([])).toThrow("object is not an object type!");
+});

Sprint-2/implement/lookup.js

@@ -1,5 +1,5 @@
-function createLookup() {
-  // implementation here
+function createLookup(arrayPairs) {
+  return Object.fromEntries(arrayPairs);
 }
 
 module.exports = createLookup;

Sprint-2/implement/lookup.test.js

@@ -1,6 +1,20 @@
 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 arrayPairs = [
+    ["US", "USD"],
+    ["CA", "CAD"],
+  ];
+
+  const object = {
+    US: "USD",
+    CA: "CAD",
+  };
+
+  const result = createLookup(arrayPairs);
+
+  expect(result).toEqual(object);
+});
 
 /*
 

Sprint-2/implement/querystring.js

@@ -1,12 +1,11 @@
 function parseQueryString(queryString) {
   const queryParams = {};
-  if (queryString.length === 0) {
-    return queryParams;
-  }
-  const keyValuePairs = queryString.split("&");
 
-  for (const pair of keyValuePairs) {
-    const [key, value] = pair.split("=");
+  if (!queryParams) return queryParams;
+
+  const searchParameters = new URLSearchParams(queryString);
+
+  for (const [key, value] of searchParameters.entries()) {
     queryParams[key] = value;
   }
 

Sprint-2/implement/querystring.test.js

@@ -3,10 +3,100 @@
 // 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",
-  });
+// Verifies that raw '+' characters are interpreted as spaces by URLSearchParams
+test("parses query string values with unencoded '+' as spaces", () => {
+  const result = parseQueryString("equation=x=y+1");
+  const output = { equation: "x=y 1" }; // because URLSearchParams decodes '+' as a space according to URL encoding rules
+  expect(result).toEqual(output);
+});
+
+// Verifies that properly URL-encoded '=' and '+' characters are preserved correctly
+test("parses query string values with encoded '=' and '+' correctly", () => {
+  const result = parseQueryString("equation=x%3Dy%2B1"); // '%3D' => '=', '%2B' => '+'
+  const output = { equation: "x=y+1" }; // because URLSearchParams decodes percent-encoded characters but preserves literal '+' when encoded as '%2B'
+  expect(result).toEqual(output);
+});
+
+test("returns empty object for empty string", () => {
+  const result = parseQueryString();
+  const output = {};
+  expect(result).toEqual(output);
+});
+
+test("handles undefined input", () => {
+  const result = parseQueryString(undefined);
+  const output = {};
+  expect(result).toEqual(output);
+});
+
+test("handles null input", () => {
+  const result = parseQueryString(null);
+  const output = {};
+  expect(result).toEqual(output);
+});
+
+test("handles key without value", () => {
+  const result = parseQueryString("name=");
+  const output = { name: "" };
+  expect(result).toEqual(output);
+});
+
+test("handles missing key", () => {
+  const result = parseQueryString("=John");
+  const output = { "": "John" };
+  expect(result).toEqual(output);
+});
+
+test("handles multiple key-value pairs", () => {
+  const result = parseQueryString("name=John&age=30&city=London");
+  const output = {
+    name: "John",
+    age: "30",
+    city: "London",
+  };
+  expect(result).toEqual(output);
+});
+
+test("handles duplicate keys by overwriting previous value", () => {
+  const result = parseQueryString("tag=js&tag=web");
+  const output = { tag: "web" };
+  expect(result).toEqual(output);
+});
+
+test("handles URL-encoded characters", () => {
+  const result = parseQueryString("city=New%20York");
+  const output = { city: "New York" };
+  expect(result).toEqual(output);
+});
+
+test("handles unencoded special characters", () => {
+  const result = parseQueryString("greeting=hello world");
+  const output = { greeting: "hello world" };
+  expect(result).toEqual(output);
+});
+
+test("handles keys containing '='", () => {
+  const result = parseQueryString("a=b=c=d");
+  const output = { a: "b=c=d" };
+  expect(result).toEqual(output);
+});
+
+test("ignores leading and trailing ampersands", () => {
+  const result = parseQueryString("&name=John&age=30&");
+  const output = { name: "John", age: "30" };
+  expect(result).toEqual(output);
+});
+
+test("ignores empty pairs", () => {
+  const result = parseQueryString("name=John&&age=30&");
+  const output = { name: "John", age: "30" };
+  expect(result).toEqual(output);
+});
+
+test("handles equals sign only", () => {
+  const result = parseQueryString("=");
+  const output = { "": "" };
+  expect(result).toEqual(output);
 });

Sprint-2/implement/tally.js

@@ -1,3 +1,11 @@
-function tally() {}
+function tally(array) {
+  if (!Array.isArray(array)) throw new Error("array is not an array!");
+
+  return array.reduce((accumulator, currentValue) => {
+    const value = accumulator[currentValue];
+    accumulator[currentValue] = value ? value + 1 : 1;
+    return accumulator;
+  }, Object.create(null));
+}
 
 module.exports = tally;

Sprint-2/implement/tally.test.js

@@ -19,16 +19,35 @@ 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("output containing the count for each unique item", () => {
+  const array = ["a", "b", "c"];
+  const result = tally(array);
+  const output = { a: 1, b: 1, c: 1 };
+  expect(result).toEqual(output);
+});
 
 // 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", () => {
+  const array = [];
+  const result = tally(array);
+  expect(result).toEqual({});
+});
 
 // Given an array with duplicate items
 // When passed to tally
 // Then it should return counts for each unique item
+test("array with duplicate items", () => {
+  const array = ["a", "b", "b", "c", "c", "c"];
+  const result = tally(array);
+  const output = { a: 1, b: 2, c: 3 };
+  expect(result).toEqual(output);
+});
 
 // Given an invalid input like a string
 // When passed to tally
 // Then it should throw an error
+test("invalid input", () => {
+  expect(() => tally("Hello, World!")).toThrow("array is not an array!");
+});

Sprint-2/interpret/invert.js

@@ -7,23 +7,44 @@
 // E.g. invert({x : 10, y : 20}), target output: {"10": "x", "20": "y"}
 
 function invert(obj) {
+  if (obj === null || typeof obj !== "object") {
+    throw new Error("Parameter `obj` must be an object type");
+  }
+
   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?
 
+// Returns an array of key/values of the enumerable own properties of an object
+// It is a convenient way to map the object properties and values into key-value pairs
+
 // d) Explain why the current return value is different from the target output
 
+// Because of this line:
+// invertedObj.key = value;
+// The property "key" is declared and the value is assigned to the "key" property
+
 // e) Fix the implementation of invert (and write tests to prove it's fixed!)
+
+// Refer to invert.test.js