LONDON | May-2025 | Sisay Mehari | Module-Structuring-and-Testing-Data | Sprint-1

Sprint-1/1-key-exercises/1-count.js

@@ -4,3 +4,7 @@ count = count + 1;
 
 // Line 1 is a variable declaration, creating the count variable with an initial value of 0
 // Describe what line 3 is doing, in particular focus on what = is doing
+//Line 3 is doing: - its reads the current value of count (which is 0), 
+// then it adds 1 to that value (0 + 1 = 1)
+// then, it reassigns that result (1) back into count variable.
+// The = symbol is the assignment operator, Take the value on the right side, and store it into the variable on the left side.

Sprint-1/1-key-exercises/2-initials.js

@@ -9,3 +9,5 @@ let initials = ``;
 
 // https://www.google.com/search?q=get+first+character+of+string+mdn
 
+let initials = firstName[0] + middleName[0] + lastName[0];
+console.log(initials);

Sprint-1/1-key-exercises/3-paths.js

@@ -17,7 +17,6 @@ console.log(`The base part of ${filePath} is ${base}`);
 // Create a variable to store the dir part of the filePath variable
 // Create a variable to store the ext part of the variable
 
-const dir = ;
-const ext = ;
-
+const dir = filePath.slice(0, lastSlashIndex);
+const ext = base.slice(dotIndex);
 // https://www.google.com/search?q=slice+mdn

Sprint-1/1-key-exercises/4-random.js

@@ -2,8 +2,29 @@ const minimum = 1;
 const maximum = 100;
 
 const num = Math.floor(Math.random() * (maximum - minimum + 1)) + minimum;
+console.log(num);
 
-// In this exercise, you will need to work out what num represents?
+/// In this exercise, you will need to work out what num represents?
 // Try breaking down the expression and using documentation to explain what it means
+//num stores a random whole number in the range from the minimum value (1) to the maximum value (100), including both ends.
+// Try breaking down the expression and using documentation to explain what it means?
 // It will help to think about the order in which expressions are evaluated
 // Try logging the value of num and running the program several times to build an idea of what the program is doing
+//const num = Math.floor(Math.random() * (maximum - minimum + 1)) + minimum;  
+//This line generates a random integer between minimum and maximum, inclusive. Here's a breakdown:
+//Math.random() returns a decimal between 0 (inclusive) and 1 (exclusive).
+//→ MDN: Math.random()
+
+//(maximum - minimum + 1) defines the size of the range, including the maximum.
+
+//Multiplying the two scales the random number to a desired range.
+
+//Math.floor(...) rounds down to ensure a whole number.
+//→ MDN: Math.floor()
+
+//+ minimum shifts the range so it starts at the minimum value.
+
+// Result: num is a random integer from minimum to maximum, inclusive.
+
+//Example: If minimum = 1 and maximum = 100, num will be a random whole number between 1 and 100.
+//I added console.log(num) and ran the program multiple times. I observed that num always gives a different whole number between 1 and 100. This helped me understand that the expression creates a random integer by multiplying a random decimal by the range size, rounding down, and then shifting it by the minimum value.

Sprint-1/2-mandatory-errors/0.js

@@ -1,2 +1,3 @@
-This is just an instruction for the first activity - but it is just for human consumption
-We don't want the computer to run these 2 lines - how can we solve this problem?
+//This is just an instruction for the first activity - but it is just for human consumption
+//We don't want the computer to run these 2 lines - how can we solve this problem?
+//To make sure the computer doesn't run them, I turned them into comments using // so they’re ignored by the JavaScript engine.

Sprint-1/2-mandatory-errors/1.js

@@ -1,4 +1,6 @@
 // trying to create an age variable and then reassign the value by 1
-
-const age = 33;
+let age = 33;
 age = age + 1;
+//Or we can use like this 
+age += 1;
+console.log(age);

Sprint-1/2-mandatory-errors/2.js

@@ -1,5 +1,26 @@
-// Currently trying to print the string "I was born in Bolton" but it isn't working...
-// what's the error ?
+/*
+  QUESTION:
+  The following code fails to print "I was born in Bolton". What's the error?
 
-console.log(`I was born in ${cityOfBirth}`);
+  console.log(`I was born in ${cityOfBirth}`);
+  const cityOfBirth = "Bolton";
+
+  ANSWER:
+  The error occurs because:
+  1. We're trying to use 'cityOfBirth' before it's declared
+  2. const/let variables can't be accessed before declaration (Temporal Dead Zone)
+
+  SOLUTION:
+  const cityOfBirth = "Bolton"; // Declare first
+  console.log(`I was born in ${cityOfBirth}`); // Now works
+
+  EXPLANATION:
+  - Order matters in JavaScript for const/let variables
+  - The fixed version follows proper variable declaration order
+  - This avoids the Temporal Dead Zone reference error
+  - Output will now correctly show: "I was born in Bolton"
+*/
+
+// Corrected implementation:
 const cityOfBirth = "Bolton";
+console.log(`I was born in ${cityOfBirth}`);

Sprint-1/2-mandatory-errors/3.js

@@ -3,7 +3,21 @@ const last4Digits = cardNumber.slice(-4);
 
 // The last4Digits variable should store the last 4 digits of cardNumber
 // However, the code isn't working
+
 // Before running the code, make and explain a prediction about why the code won't work
+// 1. Why does it give this error?
+// The error occurs because cardNumber is a number, and numbers don't have the .slice() method. The .slice() method works on strings or arrays.
+
 // Then run the code and see what error it gives.
 // Consider: Why does it give this error? Is this what I predicted? If not, what's different?
+// 2. Is this what I predicted?
+// Not exactly. I initially thought the problem was with the argument -4 inside .slice(), maybe it should have been just 4. I did not predict that the issue was with using .slice() on a number instead of a string.
+
+// 3. What's different?
+// The actual issue is that .slice() is not a method for numbers at all, so we must convert the number to a string before slicing.
+
 // Then try updating the expression last4Digits is assigned to, in order to get the correct value
+// 4. How did I update the expression to get the correct value?
+// I fixed it by converting the number to a string using .toString(), then applying .slice(-4) on the string:
+const correctedLast4Digits = cardNumber.toString().slice(-4);
+console.log(`The last 4 digits of the card number are ${correctedLast4Digits}`);

Sprint-1/2-mandatory-errors/4.js

@@ -1,2 +1,22 @@
-const 12HourClockTime = "20:53";
-const 24hourClockTime = "08:53";
+// Problem Case (invalid syntax):
+// const 12HourClockTime = "20:53";  // ❌ SyntaxError: Invalid variable name
+// const 24hourClockTime = "08:53";  // ❌ Also invalid (starts with number)
+
+// Solution:
+const twelveHourClockTime = "08:53";  // ✅ Valid (starts with letter)
+const twentyFourHourClockTime = "20:53";  // ✅ Valid
+
+/* Explanation:
+1. JavaScript variable naming rules:
+   - Cannot start with a digit (0-9)
+   - Must start with letter, underscore (_), or dollar sign ($)
+
+2. Fix approach:
+   - Changed numeric prefixes to words ("twelve" instead of 12)
+   - Maintained clear, descriptive names
+   - Kept the same time values as strings
+
+3. Why strings are appropriate:
+   - Time formats with colons are best represented as strings
+   - No arithmetic operations needed on these values
+*/

Sprint-1/3-mandatory-interpret/1-percentage-change.js

@@ -2,7 +2,8 @@ let carPrice = "10,000";
 let priceAfterOneYear = "8,543";
 
 carPrice = Number(carPrice.replaceAll(",", ""));
-priceAfterOneYear = Number(priceAfterOneYear.replaceAll("," ""));
+priceAfterOneYear = Number(priceAfterOneYear.replaceAll("," "")); // This line has the error
+priceAfterOneYear = Number(priceAfterOneYear.replaceAll(",", "")); // This line was added in your example
 
 const priceDifference = carPrice - priceAfterOneYear;
 const percentageChange = (priceDifference / carPrice) * 100;
@@ -11,12 +12,55 @@ console.log(`The percentage change is ${percentageChange}`);
 
 // Read the code and then answer the questions below
 
-// a) How many function calls are there in this file? Write down all the lines where a function call is made
+/*
+a) How many function calls are there in this file? Write down all the lines where a function call is made
+*/
+// There are 7 function calls in this file. They are:
+// Line 4:
+//   carPrice.replaceAll(",", "") → Calls the replaceAll() method on the carPrice string.
+//   Number(...) → Converts the result to a number using the Number() function.
+// Line 5:
+//   priceAfterOneYear.replaceAll(",", "") → Calls the replaceAll() method on priceAfterOneYear.
+//   Number(...) → Converts the result to a number using the Number() function.
+// Line 6:
+//   priceAfterOneYear.replaceAll(",", "") → Calls the replaceAll() method on priceAfterOneYear.
+//   Number(...) → Converts the result to a number using the Number() function.
+// Line 10:
+//   console.log(...) → Calls the log() function to print to the console.
 
-// b) Run the code and identify the line where the error is coming from - why is this error occurring? How can you fix this problem?
+/*
+b) Run the code and identify the line where the error is coming from - why is this error occurring? How can you fix this problem?
+*/
+// The error occurs on Line 5:
+// priceAfterOneYear = Number(priceAfterOneYear.replaceAll("," ""));
+// because the replaceAll() method is missing a comma between its two arguments. It should be:
+// priceAfterOneYear.replaceAll(",", "")
+// The fix is to add the comma between the arguments to make it syntactically correct.
 
-// c) Identify all the lines that are variable reassignment statements
+/*
+c) Identify all the lines that are variable reassignment statements
+*/
+// The variables carPrice and priceAfterOneYear are reassigned on lines 4, 5, and 6:
+// carPrice = Number(carPrice.replaceAll(",", "")); // Line 4
+// priceAfterOneYear = Number(priceAfterOneYear.replaceAll(",", "")); // Line 5 (assuming fixed)
+// priceAfterOneYear = Number(priceAfterOneYear.replaceAll(",", "")); // Line 6
+// These lines update the existing variables by converting their string values (with commas) into numbers without commas.
 
-// d) Identify all the lines that are variable declarations
+/*
+d) Identify all the lines that are variable declarations
+*/
+// The variable declarations happen on the following lines:
+// Line 1: let carPrice = "10,000";
+// Line 2: let priceAfterOneYear = "8,543";
+// Line 8: const priceDifference = carPrice - priceAfterOneYear;
+// Line 9: const percentageChange = (priceDifference / carPrice) * 100;
+// So, there are 4 variable declarations in total.
 
-// e) Describe what the expression Number(carPrice.replaceAll(",","")) is doing - what is the purpose of this expression?
+/*
+e) Describe what the expression Number(carPrice.replaceAll(",","")) is doing - what is the purpose of this expression?
+*/
+// The expression Number(carPrice.replaceAll(",", "")) performs two tasks:
+// 1. carPrice.replaceAll(",", ""): This removes all commas from the carPrice string.
+//    For example, if carPrice = "10,000", this part of the expression turns it into "10000".
+// 2. Number(...): This then converts the cleaned string "10000" into a number: 10000.
+// This expression is used to convert a string that looks like a number with commas (like "10,000") into an actual number (10000) so that it can be used in mathematical calculations.

Sprint-1/3-mandatory-interpret/2-time-format.js

@@ -11,15 +11,54 @@ console.log(result);
 
 // For the piece of code above, read the code and then answer the following questions
 
-// a) How many variable declarations are there in this program?
+/*
+a) How many variable declarations are there in this program?
+*/
+// There are 6 variable declarations in the program. Each is declared using the const keyword:
+// 1. const movieLength = 8784;
+// 2. const remainingSeconds = movieLength % 60;
+// 3. const totalMinutes = (movieLength - remainingSeconds) / 60;
+// 4. const remainingMinutes = totalMinutes % 60;
+// 5. const totalHours = (totalMinutes - remainingMinutes) / 60;
+// 6. const result = `${totalHours}:${remainingMinutes}:${remainingSeconds}`;
 
-// b) How many function calls are there?
+/*
+b) How many function calls are there?
+*/
+// There is 1 function call in this program:
+// console.log(result); → This is a call to the console.log() function, which outputs the value of result to the console.
 
-// c) Using documentation, explain what the expression movieLength % 60 represents
-// https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Arithmetic_Operators
+/*
+c) Using documentation, explain what the expression movieLength % 60 represents
+https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Arithmetic_Operators
+*/
+// The expression movieLength % 60 uses the modulus operator %, which returns the remainder after dividing one number by another.
+// It calculates how many seconds are left over after converting the total movieLength (in seconds) into whole minutes.
+// So, if movieLength is 8784 seconds, 8784 % 60 gives 24, meaning 24 seconds remain after making as many full minutes as possible.
+// Reference: MDN Docs - Modulus operator
 
-// d) Interpret line 4, what does the expression assigned to totalMinutes mean?
+/*
+d) Interpret line 4, what does the expression assigned to totalMinutes mean?
+*/
+// Line 4 calculates the total number of full minutes in the movie length by subtracting the remaining seconds from the total seconds and then dividing by 60.
+// const totalMinutes = (movieLength - remainingSeconds) / 60;
+// This ensures that only complete minutes are counted, ignoring the leftover seconds.
+// For example, if movieLength is 8784 seconds and remainingSeconds is 24, then:
+// totalMinutes = (8784 - 24) / 60 = 8760 / 60 = 146 minutes.
 
-// e) What do you think the variable result represents? Can you think of a better name for this variable?
+/*
+e) What do you think the variable result represents? Can you think of a better name for this variable?
+*/
+// The variable result represents the movie length formatted as a string in hh:mm:ss (hours, minutes, seconds) format.
+// A better name for this variable could be:
+// movieDurationFormatted (or movieTimeFormatted)
+// This would make the purpose of the variable more clear when reading the code.
 
-// f) Try experimenting with different values of movieLength. Will this code work for all values of movieLength? Explain your answer
+/*
+f) Try experimenting with different values of movieLength. Will this code work for all values of movieLength? Explain your answer
+*/
+// Yes, the code works for various non-negative integer values of movieLength. For example:
+// When movieLength = 59, the result is 0:0:59, which is correct.
+// When movieLength = 732, the result is 0:12:12, which is also accurate.
+// The code handles the conversion from seconds to hours, minutes, and seconds properly for different input values.
+// (Note: The code assumes movieLength is a non-negative integer. It would produce decimal results or unexpected formats for negative or non-integer inputs, but for typical movie lengths, it works.)

Sprint-1/3-mandatory-interpret/3-to-pounds.js

@@ -25,3 +25,21 @@ console.log(`£${pounds}.${pence}`);
 
 // To begin, we can start with
 // 1. const penceString = "399p": initialises a string variable with the value "399p"
+// This value represents a monetary amount in pence, with a trailing "p" to indicate "pence" (e.g., 399 pence).
+// 2. const penceStringWithoutTrailingP = penceString.substring(0, penceString.length - 1);
+// This line removes the last character ("p") from the penceString.
+// It uses .substring() to extract all characters from index 0 up to (but not including) the final character.
+// Purpose: To isolate the numeric portion of the string so that calculations can be performed.
+// 3. const paddedPenceNumberString = penceStringWithoutTrailingP.padStart(3, "0");
+// This line ensures the string has at least 3 characters by adding "0" to the start if it's too short.
+// Rationale: This guarantees that the number has enough digits to split correctly into pounds and pence, even if the original number is small (e.g., "5p" becomes "005").
+// 4. const pounds = paddedPenceNumberString.substring(0, paddedPenceNumberString.length - 2);
+// This line extracts the pounds part by slicing the string from the beginning up to the last 2 characters.
+// Rationale: In UK currency, the last two digits represent pence, and the digits before that represent pounds.
+// 5. const pence = paddedPenceNumberString.substring(paddedPenceNumberString.length - 2).padEnd(2, "0");
+// This line extracts the last 2 characters as the pence part.
+// If for any reason it's shorter than 2 digits, it adds a "0" to the end to ensure the format is correct.
+// Purpose: Guarantees a consistent two-digit pence value.
+// 6. console.log(`£${pounds}.${pence}`);
+// This line constructs and prints the final price string in pounds and pence format, using template literals.
+// Rationale: This is the output the user will see, displaying the price in standard British currency format (e.g., £3.99).

Sprint-1/4-stretch-explore/chrome.md

@@ -7,12 +7,27 @@ Just like the Node REPL, you can input JavaScript code into the Console tab and
 
 Let's try an example.
 
-In the Chrome console,
-invoke the function `alert` with an input string of `"Hello world!"`;
+I// invoke the function alert with an input string of "Hello world!";
 
-What effect does calling the `alert` function have?
+// What effect does calling the alert function have?
+// When the alert("Hello world!") function is called in the Chrome console,
+// a popup dialog box appears in the browser window with the message:
+//                Hello world!
+// The user must click “OK” to close the alert and continue using the page.
+// It pauses interaction with the page until it is dismissed.
 
-Now try invoking the function `prompt` with a string input of `"What is your name?"` - store the return value of your call to `prompt` in an variable called `myName`.
 
-What effect does calling the `prompt` function have?
-What is the return value of `prompt`?
+// Now try invoking the function prompt with a string input of "What is your name?" - store the return value of your call to prompt in an variable called myName.
+// let myName = prompt("What is your name?");
+
+// What effect does calling the prompt function have?
+// A dialog box appears asking the user to enter some text.
+// The user sees the message:
+//         What is your name?
+// and there is a text input field and buttons OK and Cancel.
+
+// What is the return value of prompt?
+// The function returns a string containing whatever the user typed.
+// For example, if the user typed Sisay and presses OK:
+//         myName  // is now equal to "Sisay"
+// (Also, if the user clicks "Cancel" or presses Escape, the function returns null.)