London | 26-ITP-Jan | Kayanat Suleman | Sprint 2 | Data Groups

Sprint-2/debug/address.js

@@ -1,4 +1,7 @@
 // Predict and explain first...
+//The issue with this program is that console.log is logging the address but is an object. address[0] only works for arrays. 
+//As address is an object, we must use a key rather than numeric indexes. 
+//Also there is no property called "0" inside address.
 
 // This code should log out the houseNumber from the address object
 // but it isn't working...
@@ -12,4 +15,4 @@ 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 +1,7 @@
 // Predict and explain first...
+// The issue with this program is that for.. of only works on iterable objects.
+// Plain JavaScript objects are not iterable, so this will throw a "TypeError".
+// To fix this, we can use Object.values(author) which converts the object's value into an array.
 
 // 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 +14,6 @@ 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 +1,9 @@
 // Predict and explain first...
+//The issue with this program is that ${recipe} inserts the entire object into the template string.
+// When an object is converted to a string, it becomes "[object Object]".
+//Instead we would need to access the ingredients array.
+//We can loop through recipe.ingredients or use join("\n")
+//This will print each ingredients 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 +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 +1,10 @@
-function contains() {}
-
+function contains(object, propertyName) {
+if (
+    typeof object !== "object" || 
+    object === null ||
+    Array.isArray(object)) {
+    return false;
+    }
+    return propertyName in object;
+}
 module.exports = contains;

Sprint-2/implement/contains.test.js

@@ -20,16 +20,27 @@ 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("returns false for empty object", () => {
+  expect(contains({}, "a")).toBe(false);
+});
 
 // Given an object with properties
 // When passed to contains with an existing property name
 // Then it should return true
+test("returns true when object contains property", () => {
+  expect(contains({ a: 1, b: 2 }, "a")).toBe(true);
+});
 
 // Given an object with properties
 // When passed to contains with a non-existent property name
 // Then it should return false
+test("returns false when object does not contain property", () => {
+  expect(contains({ a: 1, b: 2 }, "c")).toBe(false);
+});
 
 // Given invalid parameters like an array
 // When passed to contains
 // Then it should return false or throw an error
+test("returns false for invalid input (array)", () => {
+    expect(contains(["a", "b"], "a")).toBe(false);
+});

Sprint-2/implement/lookup.js

@@ -1,5 +1,12 @@
-function createLookup() {
-  // implementation here
+function createLookup(pairs) {
+const result = {};
+for (const pair of pairs) {
+  const countryCode = pair[0];
+  const currencyCode = pair[1];
+  result[countryCode] = currencyCode;
+}
+
+return result;
 }
 
 module.exports = createLookup;

Sprint-2/implement/lookup.test.js

@@ -1,6 +1,12 @@
 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 input = [['US', 'USD'], ['CA', 'CAD']];
+  expect(createLookup(input)).toEqual({
+    US: 'USD',
+    CA: 'CAD'
+  });
+});
 
 /*
 

Sprint-2/implement/querystring.js

@@ -1,12 +1,22 @@
 function parseQueryString(queryString) {
   const queryParams = {};
+
   if (queryString.length === 0) {
     return queryParams;
   }
+
   const keyValuePairs = queryString.split("&");
 
   for (const pair of keyValuePairs) {
-    const [key, value] = pair.split("=");
+    const equalsIndex = pair.indexOf("=");
+
+    if (equalsIndex === -1) {
+      queryParams[pair] = "";
+      continue;
+    }
+    const key = pair.slice(0, equalsIndex);
+    const value = pair.slice(equalsIndex + 1);
+
     queryParams[key] = value;
   }
 

Sprint-2/implement/querystring.test.js

@@ -10,3 +10,23 @@ test("parses querystring values containing =", () => {
     "equation": "x=y+1",
   });
 });
+
+// Empty Input
+test("returns empty object for empty string", () => {
+  expect(parseQueryString("")).toEqual({});
+});
+
+// Normal single pair
+test("parses a single key/value pair", () => {
+  expect(parseQueryString("a=1")).toEqual({ a: "1" });
+});
+
+// Normal multiple pairs
+test("parses multiple key/value pairs", () => {
+  expect(parseQueryString("a=1&b=2")).toEqual({ a: "1", b: "2" });
+});
+
+// Empty value should be an empty string
+test("handles a key with an empty value", () => {
+  expect(parseQueryString("a=")).toEqual({ a: "" });
+});

Sprint-2/implement/tally.js

@@ -1,3 +1,17 @@
-function tally() {}
+function tally(items) {
+    if (!Array.isArray(items)){
+        throw new Error("Input must be an array");
+    }
+    const result = {};
+
+    for (const item of items) {
+        if (result[item]) {
+            result[item] += 1;
+        } else {
+            result[item] = 1;
+        }
+    }
+    return result;
+    }
 
 module.exports = tally;

Sprint-2/implement/tally.test.js

@@ -23,12 +23,24 @@ 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 frequency of items in array", () => {
+  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("throws error for invalid input", () => {
+  expect(() => tally("abc")).toThrow();
+});

Sprint-2/interpret/invert.js

@@ -10,20 +10,31 @@ 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 }
+// The current return value when invert is called with { a : 1 } is { key: 1 }
 
 // b) What is the current return value when invert is called with { a: 1, b: 2 }
+// When calling invert({ a: 1, b: 2 }); the loop runs twice, the first iteration outputs invertedObj.key = 1l
+// The second iterations overwrites the first, so the current value returned is { key: 2 }
 
 // c) What is the target return value when invert is called with {a : 1, b: 2}
+// The target output should swap keys and value, therefore the output (using Node REPL) after the fix is { '1': 'a', '2': 'b' }
+// After fixing the bug in the code. The values become keys, and the keys become the values. 
+// Object keys are stored as strings. 
 
-// 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({ a: 1, b: 2}) return [["a", 1]], ["b", 2]]
+// It is needed because objects are not iterable with for...of, but the entries array is, so we can loop key/value pairs.
 
-// d) Explain why the current return value is different from the target output
+// e) Explain why the current return value is different from the target output
+// In the code (before the bug fix) invertedObj.key = value creates a literal property called "key" each time, overwriting it.
+// It does not use the variable key/value for dynamic property names, so it can't swap keys and values correctly.
 
-// e) Fix the implementation of invert (and write tests to prove it's fixed!)
+// f) Fix the implementation of invert (and write tests to prove it's fixed!)

Sprint-2/interpret/invert.test.js

@@ -0,0 +1,16 @@
+const invert = require("./invert.js");
+
+test("inverts a single key value pair", () => {
+    expect(invert({ a: 1 })).toEqual({ "1": "a" });
+});
+
+test("inverts multiple key value pairs", () => {
+    expect(invert({ a: 1, b: 2 })).toEqual({ 
+        "1": "a", 
+        "2": "b"
+    });
+});
+
+test("returns empty object when given empty object", () => {
+  expect(invert({})).toEqual({});
+});