London | 26-ITP-January | Laura C | Sprint 2 | Data Groups

Sprint-2/debug/address.js

@@ -1,5 +1,9 @@
 // Predict and explain first...
 
+// Prediction: address is an object, not an array.
+// Using address[0] will return undefined because objects are accessed using keys, not indexes.
+// So the output will be: "My house number is undefined"
+
 // This code should log out the houseNumber from the address object
 // but it isn't working...
 // Fix anything that isn't working
@@ -12,4 +16,4 @@ 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

@@ -1,5 +1,10 @@
 // Predict and explain first...
 
+// Prediction: This code will throw an error.
+// The error happens because "author is an object and objects are not iterable.
+// The "for...of" loop only works with iterable objects like arrays or strings
+// So the program will throw a type error
+
 // 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 +16,7 @@ const author = {
   alive: true,
 };
 
-for (const value of author) {
-  console.log(value);
+for (const key in author) {
+  console.log(author[key]);
 }
+

Sprint-2/debug/recipe.js

@@ -1,5 +1,10 @@
 // Predict and explain first...
 
+// Prediction: The program may print [object Object]" instead of the ingredients.
+// This happens because recipe is an object, and printing an object inside a string
+// converts it to "[object Object]".
+// The ingredients array should be printed instead, with 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
 // How can you fix it?
@@ -11,5 +16,5 @@ const recipe = {
 };
 
 console.log(`${recipe.title} serves ${recipe.serves}
-  ingredients:
-${recipe}`);
+ingredients:
+${recipe.ingredients.join("\n")}`);

Sprint-2/implement/contains.js

@@ -1,3 +1,9 @@
-function contains() {}
+function contains(object, propertyName) {
+  if (typeof object !== "object" || object === null || Array.isArray(object)) {
+    return false;
+  }
 
-module.exports = contains;
+  return Object.prototype.hasOwnProperty.call(object, propertyName);
+}
+
+module.exports = contains;

Sprint-2/implement/lookup.js

@@ -1,5 +1,14 @@
-function createLookup() {
-  // implementation here
+function createLookup(countryCurrencyPairs) {
+  const lookup = {};
+
+  for (const pair of countryCurrencyPairs) {
+    const country = pair[0];
+    const currency = pair[1];
+
+    lookup[country] = currency;
+  }
+
+  return lookup;
 }
 
-module.exports = createLookup;
+module.exports = createLookup;

Sprint-2/implement/querystring.js

@@ -3,14 +3,16 @@ function parseQueryString(queryString) {
   if (queryString.length === 0) {
     return queryParams;
   }
+
   const keyValuePairs = queryString.split("&");
 
   for (const pair of keyValuePairs) {
-    const [key, value] = pair.split("=");
+    const [key, ...rest] = pair.split("=");
+    const value = rest.join("=");
     queryParams[key] = value;
   }
 
   return queryParams;
 }
 
-module.exports = parseQueryString;
+module.exports = parseQueryString;

Sprint-2/implement/tally.js

@@ -1,3 +1,23 @@
-function tally() {}
+function tally(items) {
+  if (!Array.isArray(items)) {
+    throw new Error("Input must be an array");
+  }
 
-module.exports = tally;
+  if (items.length === 0) {
+    return {};
+  }
+
+  const counts = {};
+
+  for (const item of items) {
+    if (counts[item]) {
+      counts[item] += 1;
+    } else {
+      counts[item] = 1;
+    }
+  }
+
+  return counts;
+}
+
+module.exports = tally;

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 }
+// With the buggy implementation (invertedObj.key = value), the result is:
+// { key: 1 }
 
 // b) What is the current return value when invert is called with { a: 1, b: 2 }
+// { key: 2 }
+// because the property key" is overwritten in each loop iteration
 
 // 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?
+// d) What does Object.entries return? Why is it needed in this program?
+// Object.entries(obj) returns an array of [key, value] pairs.
+// Example: Object.entries( {a:1,b:2}) → [['a',1],['b',2]]
+// It allows us to loop through both the keys and values of the object.
 
-// d) Explain why the current return value is different from the target output
-
-// e) Fix the implementation of invert (and write tests to prove it's fixed!)
+// e) Explain why the current return value is different from the target output
+// Because the buggy code used  invertedObj.key = value
+// which creates a property literally called "key
+// Instead, we need to use  invertedObj[value] = key to swap keys and values