London | May-2025 | Ikenna Agulobi | Data Groups | sprint-2

.gitignore

@@ -3,3 +3,4 @@ node_modules
 .vscode
 **/.DS_Store
 .idea
+prep-for-data-groups-module/

Sprint-2/debug/address.js

@@ -1,4 +1,5 @@
 // Predict and explain first...
+// The output will be undefined because we don't access object properties by index.
 
 // This code should log out the houseNumber from the address object
 // but it isn't working...
@@ -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

@@ -1,4 +1,5 @@
 // Predict and explain first...
+// The code will print an error because in JS we cannot iterate directly on author object. To access the values of author we need to use Object.values() method.
 
 // 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 +12,6 @@ const author = {
   alive: true,
 };
 
-for (const value of author) {
+for (const value of Object.values(author)) {
   console.log(value);
 }

Sprint-2/debug/recipe.js

@@ -1,4 +1,5 @@
 // Predict and explain first...
+//In this code, recipe.title and recipe.serves will execute as expected but ingredients: recipe will not execute as expected because we are printing out the entire recipe object. Instead What we want to do is log each ingredient on a new line.
 
 // This program should log out the title, how many it serves and the ingredients.
 // Each ingredient should be logged on a new line
@@ -11,5 +12,7 @@ const recipe = {
 };
 
 console.log(`${recipe.title} serves ${recipe.serves}
-  ingredients:
-${recipe}`);
+ingredients:`);
+for(const ingredient of recipe.ingredients){
+  console.log(`- ${ingredient}`)
+}

Sprint-2/implement/contains.js

@@ -1,3 +1,15 @@
-function contains() {}
+function contains(obj, property) {
+  //return false or throw error if parameters are invalid
+  if (typeof obj !== "object" || Array.isArray(obj) || obj === null) {
+    return false;
+  }
+  //check that the obj contains a property, and the property is not inherited.
+  //N:B Object.hasOwn() strictly check for own properties and not inherited ones.
+  if (Object.hasOwn(obj, property)) {
+    return true;
+  } else {
+    return false;
+  }
+}
 
 module.exports = contains;

Sprint-2/implement/contains.test.js

@@ -1,4 +1,4 @@
-const contains = require("./contains.js");
+const contains = require("./contains");
 
 /*
 Implement a function called contains that checks an object contains a
@@ -16,20 +16,39 @@ 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("Given an object and a property name, should return true if object contains the property otherwise false", () => {
+  const obj = { a: 1, b: 2 };
+  const property = "a";
+  expect(contains(obj, property)).toEqual(true);
+});
 // Given an empty object
 // When passed to contains
 // Then it should return false
-test.todo("contains on empty object returns false");
+
+test("contains should returns false for an empty object", () => {
+  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("object passed to contains with an existing property name, should return true", () => {
+  const obj = { a: 1, b: 2 };
+  const property = "b";
+  expect(contains(obj, property)).toEqual(true);
+});
 
 // Given an object with properties
 // When passed to contains with a non-existent property name
 // Then it should return false
-
+test("When object passed to contains with non existent property name, should return false", () => {
+  const obj = { a: 1, b: " " };
+  const property = " ";
+  expect(contains(obj, property)).toEqual(false);
+});
 // Given invalid parameters like an array
 // When passed to contains
 // Then it should return false or throw an error
+test("When invalid parameters like array are passed to contains, should return false or throw error", () => {
+  expect(contains([], 'c')).toEqual(false);
+});

Sprint-2/implement/lookup.js

@@ -1,5 +1,11 @@
-function createLookup() {
-  // implementation here
+function createLookup(countryCodes) {
+  const countryCodeAndCurrency = {};
+  //Iterating over the array to access the inner arrays
+  for(const item of countryCodes){
+    countryCodeAndCurrency[item[0]] = item[1]
+  }
+  return countryCodeAndCurrency;
 }
+console.log(createLookup([["US", "USD"],["CA", "CAD"]]));
 
 module.exports = createLookup;

Sprint-2/implement/lookup.test.js

@@ -1,6 +1,19 @@
 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 countryCodeAndCurrency = [["US", "USD"],["CA", "CAD"]];
+  const expectedReturn = {US: "USD",CA: "CAD"};
+  const lookupFunction = createLookup(countryCodeAndCurrency);
+  expect(lookupFunction).toEqual(expectedReturn);
+});
+
+//should return an empty object when given an empty array
+test("should return an empty object when given an empty array", () => {
+  const emptyArray  = [];
+  const lookupFunction = createLookup(emptyArray);
+  expect(lookupFunction).toEqual({});
+});
+
 
 /*
 

Sprint-2/implement/querystring.js

@@ -1,15 +1,32 @@
 function parseQueryString(queryString) {
   const queryParams = {};
+
+  if (typeof queryString !== "string") {
+    throw new Error("Your input is not valid");
+  }
+
   if (queryString.length === 0) {
     return queryParams;
   }
+
   const keyValuePairs = queryString.split("&");
 
   for (const pair of keyValuePairs) {
-    const [key, value] = pair.split("=");
-    queryParams[key] = value;
+    //get the indexof the first occurrence of "="
+    const index = pair.indexOf("=");
+    //slice the first part and store in a variable
+    const slicedFirstPart = pair.slice(0, index);
+    //get the second part and store in a variable
+    const slicedSecondPart = pair.slice(index + 1);
+    //decoding the key value pairs e.g ("a%25b=c%26d") results in { "a%b": "c&d" }
+    const decodeKey = decodeURIComponent(slicedFirstPart);
+    const decodeValue = decodeURIComponent(slicedSecondPart);
+
+    //then add it to the queryParams 
+    queryParams[decodeKey] = decodeValue;
   }
 
+
   return queryParams;
 }
 

Sprint-2/implement/querystring.test.js

@@ -10,3 +10,17 @@ test("parses querystring values containing =", () => {
     "equation": "x=y+1",
   });
 });
+
+
+
+test(" when invalid strings are passed, should throw an error", () => {
+  expect(() => parseQueryString(123)).toThrow("Your input is not valid");
+  expect(() => parseQueryString({})).toThrow("Your input is not valid");
+  expect(() => parseQueryString([])).toThrow("Your input is not valid");
+});
+
+// When empty strings are passed, should return empty object
+
+test("When empty strings are passed, should return empty object", () => {
+  expect(parseQueryString("")).toEqual({});
+});

Sprint-2/implement/tally.js

@@ -1,3 +1,32 @@
-function tally() {}
-
+function tally(list) {
+  const countItem = {};
+//Throw new error if type is not array
+  if (!Array.isArray(list)) {
+    throw new Error("Your input is invalid!");
+  }
+//return empty object if array is empty
+  if(list.length === 0){
+    return {}
+  }
+//Loop through the array and count how many times each item occurs.
+  for (let i = 0; i < list.length; i++) {
+    let currentItem = list[i];
+    //if the current item exist, increment its count by 1.
+    if (countItem[currentItem]) {
+      countItem[currentItem] ++;
+    } else {
+      //Otherwise initial its count by 1
+      countItem[currentItem] = 1;
+    }
+  }
+  return countItem;
+}
+// let call1 = tally("");
+// let call2 = tally(["a", "a", "b", "a","c"]);
+// let call3 = tally(["a", "a", "a", "b", "z", "z"]);
+// let call4 = tally(["a", "a"]);
+// // console.log(call1);
+// // console.log(call2);
+// // console.log(call3);
+// // console.log(call4);
 module.exports = tally;

Sprint-2/implement/tally.test.js

@@ -19,16 +19,28 @@ 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("When passed an array of items, returns an object containing the count for each unique item", () => {
+  expect(tally(["a"])).toEqual({ a: 1 });
+  expect(tally(["a", "a", "a"])).toEqual({ a: 3 });
+});
 
 // 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("When passed an array with duplicate items, returns count for each unique item", () => {
+  expect(tally(["a", "a", "b", "c"])).toEqual({ a: 2, b: 1, c: 1 });
+});
 
 // Given an invalid input like a string
 // When passed to tally
 // Then it should throw an error
+test("When invalid input like string, throw an error ", () => {
+  expect(() => tally("")).toThrow("Your input is invalid!");
+});

Sprint-2/interpret/invert.js

@@ -9,21 +9,32 @@
 function invert(obj) {
   const invertedObj = {};
 
+  if(typeof obj !== "object" || Array.isArray(obj)){
+    throw new Error("Your input is invalid!")
+  }
+
   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 }
+// let call1 = invert([]);
+// let call2 = invert({ a: 1, b: 2});
+// console.log(call1)
+// console.log(call2)
 
-// b) What is the current return value when invert is called with { a: 1, b: 2 }
 
+module.exports = invert;
+// a) What is the current return value when invert is called with { a : 1 }
+// The return value is { key: 1 }
+// b) What is the current return value when invert is called with { a: 1, b: 2 }
+// The return value is { key: 2 }
 // c) What is the target return value when invert is called with {a : 1, b: 2}
-
+// The target return value is { '1': 'a', '2': 'b' }
 // c) What does Object.entries return? Why is it needed in this program?
-
+// Object.entries returns an array of key/value pairs of the same object and each pair is also an array with two elements(key and value). We need it in this program so that it will enable us to loop through the array and invert the items.
 // d) Explain why the current return value is different from the target output
-
+//The current return value is different from the target output because the code uses .key instead of [key]. Given that we are using .key, it gets interpreted as a property literal called "key" and not the value stored in the variable key. This causes the invert object to only have a single key called "key". To fix it and get the desired output, we need to use [key] so that the value it's storing can be use as property name when creating the new object.
 // e) Fix the implementation of invert (and write tests to prove it's fixed!)

Sprint-2/interpret/invert.test.js

@@ -0,0 +1,24 @@
+// const invert = require("./invert.js")
+const invert = require("./invert.js");
+
+
+//Given a function invert
+// When passed an object and a property name
+// Then it should return the inverted object
+test("", () => {
+expect(invert({ a: 1 })).toEqual({ '1': 'a' });
+});
+
+// Given an empty object
+// When passed to invert
+// Then it should return an empty object
+test("When passed an empty object to invert, should return an empty object", () => {
+  expect(invert({})).toEqual({});
+});
+
+// Given an invalid input,
+// When passed to invert
+// Then it should throw an error
+test("When invalid input, throw an error ", () => {
+  expect(() => invert("")).toThrow("Your input is invalid!");
+});