debug-common-errors.js

/*

Overview
In this activity, you will receive three short JavaScript programs,
each containing a different type of error (syntax, runtime, and logic)
along with a brief explanation of what the program is supposed to do.
Your task is to identify the error, correct it, and verify the fix.

Instructions
Debugging Steps:
  - Identify the error type (syntax, runtime, or logic).
  - Use Debugging Techniques such as reading error messages, using console.log(), or testing in small steps.
  - Propose a Fix that addresses the error.
  - Verify the Solution by running the code again to ensure the program works as intended.

Reflection:
Think about which debugging methods you found most useful and how you might apply them in future projects.

*/

// Programs and Solutions

// Program A
// Description:
// This program is intended to display a simple prompt in the console but fails to run.

console.log("Welcome to the bootcamp

// What’s Wrong?
//The opening double quote " for the string is there, but the closing double quote is missing.
//Also, the comment is on the same line, so JavaScript treats everything after console.log("Welcome to the bootcamp as part of the string, causing a syntax error.

//corrected code
console.log("Welcome to the bootcamp");


// Program B
// Description:
// This code attempts to multiply each number in an array by 2 and display the results. However, it crashes at runtime.

let numbers = [2, 4, "eight"];
for (let i = 0; i < numbers.length; i++) {
  let doubled = numbers[i] * 2;
  console.log(doubled);
}

// What’s Wrong?
//The issue is that the array numbers contains a string "eight" instead of a number.

//When JavaScript tries to multiply "eight" by 2, it results in NaN (Not a Number), but it does not crash; instead, it prints NaN to the console.

//So why might it "crash"?

//If your runtime environment or later code expects only numbers and does not handle NaN, it could cause problems.

//corrected code
let numbers = [2, 4, 8];  // Replace "eight" with 8
for (let i = 0; i < numbers.length; i++) {
  if (typeof numbers[i] === "number") {
    let doubled = numbers[i] * 2;
    console.log(doubled);
  } else {
    console.log(`Skipping non-number value: ${numbers[i]}`);
  }
}



// Program C (Logic Error)
// Description:
// This snippet of code is supposed to check if a given number is prime (i.e., divisible only by 1 and itself). However, it incorrectly marks some numbers as prime or not prime.

function isPrime(num) {
  if (num < 2) return false;
  for (let i = 2; i < num; i++) {
    if (num % i === 0) {
      return true;  // Supposed to indicate num is NOT prime
    }
  }
  return false; // Supposed to indicate num IS prime
}

console.log(isPrime(7)); // Expected true but gets false

// What’s Wrong?
//The logic is flipped inside the loop.
//Right now the function returns true as soon as it finds a divisor—but true is meant to mean “is prime.”
//So every composite number (like 4 or 9) is being marked as prime, and real primes (like 7) fall through to the return false at the end.

//corrected code
function isPrime(num) {
  if (num < 2) return false;
  for (let i = 2; i < num; i++) {
    if (num % i === 0) {
      return false;  // number has a divisor → not prime
    }
  }
  return true;       // no divisors found → prime
}

console.log(isPrime(7)); // true