Address mentor feedback for Sprint 2

Author: Richiealx

Sprint-2/debug/recipe.js

@@ -1,15 +1,15 @@
 // Predict and explain first...
 
 // 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?
+// Each ingredient should be logged on a new line.
+// The original code tried to print the whole object, which resulted in "[object Object]".
 
 const recipe = {
   title: "bruschetta",
   serves: 2,
   ingredients: ["olive oil", "tomatoes", "salt", "pepper"],
 };
 
-console.log(`${recipe.title} serves ${recipe.serves}
-  ingredients:
-${recipe}`);
+console.log(`${recipe.title} serves ${recipe.serves}`);
+console.log("ingredients:");
+console.log(recipe.ingredients.join("\n"));

Sprint-2/implement/contains.js

@@ -1,3 +1,20 @@
-function contains() {}
+/**
+ * contains()
+ *
+ * Checks whether an object contains a specific own property.
+ *
+ * @param {object} obj - The object to check.
+ * @param {*} propertyName - The property name to check.
+ * @returns {boolean} True if the object has the property as its own key, otherwise false.
+ */
+function contains(obj, propertyName) {
+  // Reject null, non-objects, and arrays
+  if (obj === null || typeof obj !== "object" || Array.isArray(obj)) {
+    return false;
+  }
+
+  // Object.hasOwn handles non-string property names by coercing them appropriately
+  return Object.hasOwn(obj, propertyName);
+}
 
 module.exports = contains;

Sprint-2/implement/contains.test.js

@@ -1,35 +1,37 @@
 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");
-
-// Given an object with properties
-// When passed to contains with an existing property name
-// Then it should return true
-
-// Given an object with properties
-// When passed to contains with a non-existent property name
-// Then it should return false
-
-// Given invalid parameters like an array
-// When passed to contains
-// Then it should return false or throw an error
+describe("contains()", () => {
+  test("returns false for an empty object", () => {
+    expect(contains({}, "a")).toBe(false);
+  });
+
+  test("returns true when the property exists", () => {
+    expect(contains({ a: 1, b: 2 }, "a")).toBe(true);
+  });
+
+  test("returns false when the property does not exist", () => {
+    expect(contains({ a: 1, b: 2 }, "c")).toBe(false);
+  });
+
+  test("returns false for inherited properties", () => {
+    expect(contains({ a: 1, b: 2 }, "toString")).toBe(false);
+  });
+
+  test("returns false when given an array with a realistic array key", () => {
+    expect(contains(["a", "b"], 0)).toBe(false);
+  });
+
+  test("returns false when given null", () => {
+    expect(contains(null, "a")).toBe(false);
+  });
+
+  test("supports non-string property names", () => {
+    const obj = { 3: 12 };
+    expect(contains(obj, 3)).toBe(true);
+  });
+
+  test("supports empty string as a property name", () => {
+    const obj = { "": 99 };
+    expect(contains(obj, "")).toBe(true);
+  });
+});

Sprint-2/implement/lookup.js

@@ -1,5 +1,31 @@
-function createLookup() {
-  // implementation here
+/**
+ * createLookup()
+ *
+ * Converts an array of [key, value] pairs into a lookup object.
+ *
+ * Example:
+ * [['US', 'USD'], ['CA', 'CAD']]
+ *
+ * Returns:
+ * { US: 'USD', CA: 'CAD' }
+ */
+function createLookup(pairs) {
+  if (!Array.isArray(pairs)) {
+    throw new Error("Expected an array of pairs");
+  }
+
+  const lookup = {};
+
+  for (const pair of pairs) {
+    if (!Array.isArray(pair) || pair.length !== 2) {
+      throw new Error("Each item must be a [key, value] pair");
+    }
+
+    const [key, value] = pair;
+    lookup[key] = value;
+  }
+
+  return lookup;
 }
 
 module.exports = createLookup;

Sprint-2/implement/lookup.test.js

@@ -1,35 +1,40 @@
 const createLookup = require("./lookup.js");
 
-test.todo("creates a country currency code lookup for multiple codes");
-
-/*
-
-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:
- {
-   'US': 'USD',
-   'CA': 'CAD'
- }
-*/
+describe("createLookup()", () => {
+  test("creates a country currency code lookup for multiple codes", () => {
+    const pairs = [
+      ["US", "USD"],
+      ["CA", "CAD"],
+      ["GB", "GBP"],
+    ];
+
+    expect(createLookup(pairs)).toEqual({
+      US: "USD",
+      CA: "CAD",
+      GB: "GBP",
+    });
+  });
+
+  test("returns an empty object for an empty array", () => {
+    expect(createLookup([])).toEqual({});
+  });
+
+  test("overwrites duplicate keys with the last value", () => {
+    const pairs = [
+      ["US", "USD"],
+      ["US", "USN"],
+    ];
+
+    expect(createLookup(pairs)).toEqual({
+      US: "USN",
+    });
+  });
+
+  test("throws an error when input is not an array", () => {
+    expect(() => createLookup("invalid")).toThrow();
+  });
+
+  test("throws an error when a pair is malformed", () => {
+    expect(() => createLookup([["US", "USD"], ["CA"]])).toThrow();
+  });
+});

Sprint-2/implement/querystring.js

@@ -1,12 +1,38 @@
+/**
+ * parseQueryString()
+ *
+ * Parses a query string into an object of decoded key-value pairs.
+ */
 function parseQueryString(queryString) {
-  const queryParams = {};
-  if (queryString.length === 0) {
+  const queryParams = Object.create(null);
+
+  if (typeof queryString !== "string" || queryString.length === 0) {
     return queryParams;
   }
+
   const keyValuePairs = queryString.split("&");
 
   for (const pair of keyValuePairs) {
-    const [key, value] = pair.split("=");
+    if (pair === "") {
+      continue;
+    }
+
+    const separatorIndex = pair.indexOf("=");
+
+    let rawKey;
+    let rawValue;
+
+    if (separatorIndex === -1) {
+      rawKey = pair;
+      rawValue = "";
+    } else {
+      rawKey = pair.slice(0, separatorIndex);
+      rawValue = pair.slice(separatorIndex + 1);
+    }
+
+    const key = decodeURIComponent(rawKey);
+    const value = decodeURIComponent(rawValue);
+
     queryParams[key] = value;
   }
 

Sprint-2/implement/querystring.test.js

@@ -1,12 +1,54 @@
 // In the prep, we implemented a function to parse query strings.
-// Unfortunately, it contains several bugs!
-// 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.
+// Unfortunately, it contains several bugs.
+// These tests cover the original bug and additional edge cases.
 
-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",
+describe("parseQueryString()", () => {
+  test("parses querystring values containing =", () => {
+    expect(parseQueryString("equation=x=y+1")).toEqual({
+      equation: "x=y+1",
+    });
+  });
+
+  test("returns an empty object for an empty string", () => {
+    expect(parseQueryString("")).toEqual({});
+  });
+
+  test("parses a single key-value pair", () => {
+    expect(parseQueryString("name=Richard")).toEqual({
+      name: "Richard",
+    });
+  });
+
+  test("parses multiple key-value pairs", () => {
+    expect(parseQueryString("name=Richard&city=Sheffield")).toEqual({
+      name: "Richard",
+      city: "Sheffield",
+    });
+  });
+
+  test("handles a key with an empty value", () => {
+    expect(parseQueryString("name=")).toEqual({
+      name: "",
+    });
+  });
+
+  test("handles a key with no equals sign", () => {
+    expect(parseQueryString("name")).toEqual({
+      name: "",
+    });
+  });
+
+  test("ignores an empty trailing pair", () => {
+    expect(parseQueryString("name=Richard&")).toEqual({
+      name: "Richard",
+    });
+  });
+
+  test("decodes URL-encoded keys and values", () => {
+    expect(parseQueryString("tags%5B%5D=hello%20world")).toEqual({
+      "tags[]": "hello world",
+    });
   });
 });

Sprint-2/implement/tally.js

@@ -1,3 +1,29 @@
-function tally() {}
+/**
+ * tally()
+ *
+ * Counts how many times each item appears in an array.
+ *
+ * Example:
+ * tally(["a", "a", "b", "c"])
+ * returns { a: 2, b: 1, c: 1 }
+ */
+function tally(items) {
+  if (!Array.isArray(items)) {
+    throw new Error("Expected an array");
+  }
+
+  // Create an object with no inherited properties
+  const counts = Object.create(null);
+
+  for (const item of items) {
+    if (counts[item] !== undefined) {
+      counts[item] += 1;
+    } else {
+      counts[item] = 1;
+    }
+  }
+
+  return counts;
+}
 
 module.exports = tally;