London | 26-ITP-Jan | Mohsen Zamani | sprint 2 | coursework

Sprint-2/debug/address.js

@@ -12,4 +12,8 @@ const address = {
   postcode: "XYZ 123",
 };
 
-console.log(`My house number is ${address[0]}`);
+console.log(`My house number is ${address["houseNumber"]}`);
+
+// Code returns undefined
+// because address is an object but it is accessed like an array
+// in an object values can be accessed by using their proper keys

Sprint-2/debug/author.js

@@ -11,6 +11,10 @@ const author = {
   alive: true,
 };
 
-for (const value of author) {
-  console.log(value);
+for (const key in author) {
+  console.log(author[key]);
 }
+
+// for iterating in an object for...in can be used
+// and each iteration it returns the key
+// then each value can be accessed

Sprint-2/debug/recipe.js

@@ -10,6 +10,11 @@ const recipe = {
   ingredients: ["olive oil", "tomatoes", "salt", "pepper"],
 };
 
-console.log(`${recipe.title} serves ${recipe.serves}
-  ingredients:
-${recipe}`);
+console.log(
+  `${recipe.title} serves ${recipe.serves}\ningredients:\n${recipe.ingredients.join("\n")}`
+);
+
+// everything is logged on one line
+// console.log is logging the recipe object array as a whole
+// instead of each value of ingredients array
+// the ingredients array must be logged using a loop

Sprint-2/implement/contains.js

@@ -1,3 +1,9 @@
-function contains() {}
+function contains(obj, property) {
+  if (Array.isArray(obj) || obj === null || typeof obj !== "object")
+    return false;
+
+  if (obj instanceof Map) return obj.has(property);
+  return Object.hasOwn(obj, property);
+}
 
 module.exports = contains;

Sprint-2/implement/contains.test.js

@@ -20,16 +20,29 @@ 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({}, "key1")).toEqual(false));
 
 // Given an object with properties
 // When passed to contains with an existing property name
 // Then it should return true
+test("contains returns true when object contains the given property", () =>
+  expect(contains({ key1: "value1", key2: "value2" }, "key1")).toEqual(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 when object does not contain the given property", () =>
+  expect(contains({ key1: "value1", key2: "value2" }, "key4")).toEqual(false));
 
-// Given invalid parameters like an array
+// Given parameters which are not key-value pair type
 // When passed to contains
 // Then it should return false or throw an error
+it("contains returns false or throws an error if given parameter is not a valid object", () => {
+  expect(contains([], "key1")).toEqual(false);
+  expect(contains([1, 2], 1)).toEqual(false);
+  expect(contains("key1:value1", "1")).toEqual(false);
+  expect(contains(5235, "key1")).toEqual(false);
+  expect(contains(undefined, "key1")).toEqual(false);
+  expect(contains(null, "key1")).toEqual(false);
+});

Sprint-2/implement/lookup.js

@@ -1,5 +1,9 @@
-function createLookup() {
-  // implementation here
+function createLookup(countryCurrencyPairs) {
+  if (!Array.isArray(countryCurrencyPairs)) return {};
+  return countryCurrencyPairs.reduce((acc, curr) => {
+    acc[curr[0]] = curr[1];
+    return acc;
+  }, {});
 }
 
 module.exports = createLookup;

Sprint-2/implement/lookup.test.js

@@ -1,7 +1,5 @@
 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
@@ -33,3 +31,24 @@ It should return:
    'CA': 'CAD'
  }
 */
+
+describe("createLookup", () => {
+  it("returns empty object if the parameter passed is not an array", () => {
+    expect(createLookup("US:USD")).toEqual({});
+    expect(createLookup(undefined)).toEqual({});
+  });
+
+  it("returns an object of country initials and currency code", () =>
+    expect(
+      createLookup([
+        ["US", "USD"],
+        ["CA", "CAD"],
+      ])
+    ).toEqual({
+      US: "USD",
+      CA: "CAD",
+    }));
+
+  it("returns an empty object if passed an empty array", () =>
+    expect(createLookup([])).toEqual({}));
+});

Sprint-2/implement/querystring.js

@@ -6,8 +6,28 @@ function parseQueryString(queryString) {
   const keyValuePairs = queryString.split("&");
 
   for (const pair of keyValuePairs) {
-    const [key, value] = pair.split("=");
-    queryParams[key] = value;
+    let key = "",
+      value = "";
+    let equalSignIndex = pair.indexOf("=");
+
+    if (equalSignIndex === -1) {
+      key = decodeURIComponent(pair);
+      value = "";
+    } else {
+      key = decodeURIComponent(pair.slice(0, equalSignIndex));
+      value = decodeURIComponent(pair.slice(equalSignIndex + 1));
+    }
+
+    if (key === "" && value === "") continue;
+    if (queryParams[key]) {
+      if (queryParams[key] === value) continue;
+      if (Array.isArray(queryParams[key])) {
+        queryParams[key].push(value);
+      } else {
+        const temp = queryParams[key];
+        queryParams[key] = [temp, value];
+      }
+    } else queryParams[key] = value;
   }
 
   return queryParams;

Sprint-2/implement/querystring.test.js

@@ -3,10 +3,47 @@
 // 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("parses querystring values containing repetitive keys", () => {
+  expect(parseQueryString("a=1&b=6&a=2&a=3&b=7")).toEqual({
+    a: ["1", "2", "3"],
+    b: ["6", "7"],
+  });
+});
+
+test("parses querystring values containing repetitive keys with same values", () => {
+  expect(parseQueryString("a=1&b=6&a=2&a=3&b=6")).toEqual({
+    a: ["1", "2", "3"],
+    b: "6",
+  });
+});
+
+test("parses querystring values containing no key and value but only =", () => {
+  expect(parseQueryString("=&b=6&a=2&=&=")).toEqual({
+    a: "2",
+    b: "6",
+  });
+});
+
+test("parses querystring values missing = sign", () => {
+  expect(parseQueryString("id=5&name=mohsen&age")).toEqual({
+    id: "5",
+    name: "mohsen",
+    age: "",
+  });
+});
+
+test("parses querystring with encoded keys and values", () => {
+  expect(
+    parseQueryString(
+      "search=hello%20world&city=New%20York&search=happy%20coding"
+    )
+  ).toEqual({ search: ["hello world", "happy coding"], city: "New York" });
+});

Sprint-2/implement/tally.js

@@ -1,3 +1,10 @@
-function tally() {}
+function tally(list) {
+  if (!Array.isArray(list)) throw new Error("Not an array.");
+  const obj = Object.create(null);
+  return list.reduce((acc, curr) => {
+    acc[curr] = (acc[curr] || 0) + 1;
+    return acc;
+  }, obj);
+}
 
 module.exports = tally;

Sprint-2/implement/tally.test.js

@@ -23,12 +23,23 @@ 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 on an array with duplicate items returns an object with the count of items", () => {
+  expect(tally(["a"])).toEqual({ a: 1 });
+  expect(tally(["a", "a", "b", "c"])).toEqual({ a: 2, b: 1, c: 1 });
+  expect(tally(["a", "a", "a"])).toEqual({ a: 3 });
+  expect(tally(["toString", "toString"])).toEqual({ toString: 2 });
+});
 
 // Given an invalid input like a string
 // When passed to tally
 // Then it should throw an error
+test("tally throws an error if passed not an array", () => {
+  expect(() => tally("not an array")).toThrow("Not an array.");
+  expect(() => tally({})).toThrow("Not an array.");
+});

Sprint-2/interpret/invert.js

@@ -10,20 +10,28 @@ 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 each pair of key and value as array.
+// it is needed for iteration through an object
 
 // d) Explain why the current return value is different from the target output
+// because the place of key and value are not swapped
 
 // e) Fix the implementation of invert (and write tests to prove it's fixed!)

Sprint-2/interpret/invert.test.js

@@ -0,0 +1,17 @@
+const invert = require("./invert.js");
+
+describe("invert", () => {
+  it("returns empty object if passed empty object", () =>
+    expect(invert({})).toEqual({}));
+
+  it("returns inverted object of the passed object", () => {
+    expect(invert({ a: 1, b: 2 })).toEqual({ 1: "a", 2: "b" });
+    expect(invert({ a: 1, b: 2, c: 3, d: 4, e: 5 })).toEqual({
+      1: "a",
+      2: "b",
+      3: "c",
+      4: "d",
+      5: "e",
+    });
+  });
+});

Sprint-2/stretch/count-words.js

@@ -26,3 +26,19 @@
 
 3. Order the results to find out which word is the most common in the input
 */
+
+function countWords(string) {
+  const wordArray = string
+    .toLowerCase()
+    .split(/[.,!? ]+/)
+    .filter(Boolean);
+  const wordCount = new Map();
+  for (let word of wordArray) {
+    wordCount.set(word, (wordCount.get(word) || 0) + 1);
+  }
+  const sortedWordCount = Object.fromEntries(
+    [...wordCount].sort(([wordA, countA], [wordB, countB]) => countB - countA)
+  );
+
+  return sortedWordCount;
+}

Sprint-2/stretch/mode.js

@@ -8,8 +8,8 @@
 // refactor calculateMode by splitting up the code
 // into smaller functions using the stages above
 
-function calculateMode(list) {
-  // track frequency of each value
+// track frequency of each value
+function calculateFreq(list) {
   let freqs = new Map();
 
   for (let num of list) {
@@ -19,18 +19,26 @@ function calculateMode(list) {
 
     freqs.set(num, (freqs.get(num) || 0) + 1);
   }
+  return freqs;
+}
 
-  // Find the value with the highest frequency
+// Find the value with the highest frequency
+function findMaxFreq(freqs) {
   let maxFreq = 0;
   let mode;
+
   for (let [num, freq] of freqs) {
     if (freq > maxFreq) {
       mode = num;
       maxFreq = freq;
     }
   }
+  return [maxFreq, mode];
+}
 
+function calculateMode(list) {
+  const calculatedFrequency = calculateFreq(list);
+  const [maxFreq, mode] = findMaxFreq(calculatedFrequency);
   return maxFreq === 0 ? NaN : mode;
 }
-
 module.exports = calculateMode;

Sprint-2/stretch/till.js

@@ -8,10 +8,11 @@ function totalTill(till) {
   let total = 0;
 
   for (const [coin, quantity] of Object.entries(till)) {
-    total += coin * quantity;
+    const valueOfCoin = Number(coin.slice(0, -1));
+    total += valueOfCoin * quantity;
   }
 
-  return `£${total / 100}`;
+  return `£${(total / 100).toFixed(2)}`;
 }
 
 const till = {
@@ -22,10 +23,21 @@ const till = {
 };
 const totalAmount = totalTill(till);
 
+const assertEquals = (actual, expected) => {
+  console.assert(
+    actual === expected,
+    `Received ${actual} but expected ${expected}.`
+  );
+};
+
 // a) What is the target output when totalTill is called with the till object
+// £4.4
 
 // b) Why do we need to use Object.entries inside the for...of loop in this function?
+// to iterate in an object and access the [key, value] pair
 
 // c) What does coin * quantity evaluate to inside the for...of loop?
+// it multiplies keys and values of till
 
 // d) Write a test for this function to check it works and then fix the implementation of totalTill
+assertEquals(totalAmount, "£4.40");