London |ITP-Jan-2016 | Ping Wang | Sprint 2 |Coursework

Sprint-2/debug/address.js

@@ -1,8 +1,9 @@
 // Predict and explain first...
+// it will print out My house number is undefined because the address is object rather than array so address[0] will look for property 0 which does not exit
 
 // This code should log out the houseNumber from the address object
 // but it isn't working...
-// Fix anything that isn't working
+// Fix anything that isn't working, it should be address.houseNumber in order to get value 42
 
 const address = {
   houseNumber: 42,
@@ -12,4 +13,4 @@ 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

@@ -1,7 +1,9 @@
 // Predict and explain first...
+// it will throw error or just print out undefined because 
 
 // 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
+// Because author is not array rather object so we can not use for loop, we use object.values to get loop
 
 const author = {
   firstName: "Zadie",
@@ -11,6 +13,6 @@ const author = {
   alive: true,
 };
 
-for (const value of author) {
+for (const value of Object.values(author)) {
   console.log(value);
 }

Sprint-2/debug/recipe.js

@@ -1,8 +1,9 @@
 // Predict and explain first...
+// It might print out undefined or something else
 
 // 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?
+// How can you fix it? i will loop through ingredient to get each single ingredient
 
 const recipe = {
   title: "bruschetta",
@@ -11,5 +12,5 @@ const recipe = {
 };
 
 console.log(`${recipe.title} serves ${recipe.serves}
-  ingredients:
-${recipe}`);
+ingredients:
+${recipe.ingredients.join("\n")}`);

Sprint-2/implement/contains.js

@@ -1,3 +1,15 @@
-function contains() {}
+function contains(object, property)  {
+    if (typeof object !== 'object' || object === null || Array.isArray(object)) {
+        return false;
+    }
+    return object.hasOwnProperty(property);
+}
+
+
+
+const object={name:'jin', age:13}
+
+console.log (contains(object, 'age'))
+console.log (contains(object, 'nice'))
 
 module.exports = contains;

Sprint-2/implement/contains.test.js

@@ -30,6 +30,40 @@ test.todo("contains on empty object returns false");
 // 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 function', () => {
+
+  test('returns false for an empty object', () => {
+    const object = {};
+    expect(contains({}, 'name')).toBe(false);
+  });
+
+  test('returns true when property exists', () => {
+    const object = { name: 'jin', age: 13 };
+    expect(contains(object, 'age')).toBe(true);
+  });
+
+  test('returns false when property does not exist', () => {
+    const object = { name: 'jin', age: 13 };
+    expect(contains(object, 'nice')).toBe(false);
+  });
+
+  test('returns false when input is an array', () => {
+    const object = [1, 2, 5];
+    expect(contains(object, '0')).toBe(false);
+  });
+
+  test('returns false when input is null', () => {
+    expect(contains(null, 'age')).toBe(false);
+  });
+
+  test('returns false when input is not an object', () => {
+    expect(contains(123, 'age')).toBe(false);
+    expect(contains('hello', 'length')).toBe(false);
+  });
+
+});

Sprint-2/implement/lookup.js

@@ -1,5 +1,14 @@
-function createLookup() {
-  // implementation here
+function createLookup(countryCurrencyPairs) {
+  const countryCodeCurrency = {}
+
+  for (const[country, currency] of countryCurrencyPairs) {
+   countryCodeCurrency[country] = currency
+  }
+
+  return countryCodeCurrency
 }
 
+console.log(createLookup([['GB', 'GBP']]));
+
+
 module.exports = createLookup;

Sprint-2/implement/lookup.test.js

@@ -33,3 +33,33 @@ It should return:
    'CA': 'CAD'
  }
 */
+
+// create single country currency in countryCurrencyPairs
+
+
+//given an empty country currency pair/array
+
+describe("createLookup", () => {
+
+  test("creates a country currency code lookup for multiple codes", () => {
+    const input = [['US', 'USD'], ['CA', 'CAD']];
+    const expected = { US: 'USD', CA: 'CAD' };
+
+    expect(createLookup(input)).toEqual(expected);
+  });
+
+  test("creates a single country code currency", () => {
+    const input = [['GB', 'GBP']];
+    const expected = { GB: 'GBP' };
+
+    expect(createLookup(input)).toEqual(expected);
+  });
+
+  test("returns an empty object when given an empty pair", () => {
+    const input = [[]];
+    const expected = {};
+
+    expect(createLookup(input)).toEqual(expected);
+  });
+
+});

Sprint-2/implement/querystring.js

@@ -1,16 +1,30 @@
 function parseQueryString(queryString) {
   const queryParams = {};
-  if (queryString.length === 0) {
+
+  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.includes("=")) continue; 
+
+    const equalIndex = pair.indexOf("=");
+
+    const key = pair.slice(0, equalIndex);
+    const value = pair.slice(equalIndex + 1);
+
+    if (key === "") continue;
+
     queryParams[key] = value;
   }
 
   return queryParams;
 }
 
+console.log(parseQueryString("color=blue&quality=good"))
+console.log(parseQueryString("equation=x=y+1"))
+console.log(parseQueryString(""))
+
 module.exports = parseQueryString;

Sprint-2/implement/querystring.test.js

@@ -10,3 +10,31 @@ test("parses querystring values containing =", () => {
     "equation": "x=y+1",
   });
 });
+
+//  Duplicate keys, last one wins
+test('duplicate keys overwrite previous', () => {
+  expect(parseQueryString('color=blue&color=red')).toEqual({
+    color: 'red'
+  });
+});
+
+//  Empty string input
+test('returns empty object for empty string', () => {
+  expect(parseQueryString('')).toEqual({});
+});
+
+//  Null/invalid input
+test('returns empty object for null or non-string', () => {
+  expect(parseQueryString(null)).toEqual({});
+  expect(parseQueryString(123)).toEqual({});
+});
+
+//  Missing value
+test('handles keys with empty values', () => {
+  expect(parseQueryString('empty=')).toEqual({ empty: '' });
+});
+
+// Missing key
+test('ignores pairs without keys', () => {
+  expect(parseQueryString('=novalue')).toEqual({ '': 'novalue' });
+});

Sprint-2/implement/tally.js

@@ -1,3 +1,28 @@
-function tally() {}
+function tally(array) {
+  if (!Array.isArray(array)) {
+    throw new Error("Invalid input: expected an array");
+  }
+
+  const count = Object.create(null);
+
+  for (const item of array) {
+    if (count[item]) {
+      count[item] += 1;
+    } else {
+      count[item] = 1;
+    }
+  }
+
+  return count;
+}
+
+console.log(tally([ 2,"bee",2,"apple","apple",2, "banana"]))
+
+try {
+  console.log(tally('morning'));
+} catch (err) {
+  console.error(err.message);
+}
+
 
 module.exports = tally;

Sprint-2/implement/tally.test.js

@@ -23,12 +23,51 @@ 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("counts a single item correctly", () => {
+    expect(tally(['a'])).toEqual({ a: 1 });
+});
+
+  // Repeated items
+test("counts repeated items correctly", () => {
+    expect(tally(['a', 'a', 'a'])).toEqual({ a: 3 });
+});
+
+  // Mixed items
+test("counts multiple different items", () => {
+    expect(tally(['a', 'a', 'b', 'c'])).toEqual({
+      a: 2,
+      b: 1,
+      c: 1
+    });
+});
+
+
+test("tally on single, repeated or duplicate items return counts for each unique item ", () => {
+  expect(tally([ 2,"bee",2,"apple","apple",2, "banana"])).toEqual({
+    2: 3,
+    bee: 1,
+    apple: 2,
+    banana: 1
+  });
+});
+
 // Given an invalid input like a string
 // When passed to tally
 // Then it should throw an error
+test("throws error for string input", () => {
+  expect(() => tally("morning"))
+    .toThrow("Invalid input: expected an array");
+});
+
+test("throws error for number input", () => {
+  expect(() => tally(123))
+    .toThrow();
+});

Sprint-2/interpret/invert.js

@@ -10,20 +10,29 @@ function invert(obj) {
   const invertedObj = {};
 
   for (const [key, value] of Object.entries(obj)) {
-    invertedObj.key = value;
+
+    invertedObj[value] = key;
   }
 
   return invertedObj;
 }
 
-// a) What is the current return value when invert is called with { a : 1 }
+console.log(invert({a:1, b:2, apple:4}))
+
+// a) What is the current return value when invert is called with { a : 1 } 
+// it returns {key:1}
 
 // b) What is the current return value when invert is called with { a: 1, b: 2 }
+// it returns {key:2}
 
 // c) What is the target return value when invert is called with {a : 1, b: 2}
+// the target return value should be {'1': 'a','2':'b'}
 
 // c) What does Object.entries return? Why is it needed in this program?
+// Object.entries(obj) lets  loop [key, value] pairs easily because .entries(object/array) is built in method in javascript
 
 // d) Explain why the current return value is different from the target output
+// Because invertedObj.key=value is wrong which means  key of property will be always 'key'  and value will remains the same as obj array in invertedObj
 
 // e) Fix the implementation of invert (and write tests to prove it's fixed!)
+// I put invertedObh[value]= key instead then the function works as expected