Spot the Bug: Fixing Incorrect Max Value in JavaScript

Introduction

Debugging is an essential skill in programming, and sometimes, even simple-looking functions can contain hidden bugs. Let's analyze a JavaScript function that is supposed to find the maximum value in an array. Can you spot the bug?

function findMaxValue(inputArray) {
  let maxVal = 0;
  for (let index = 0; index < inputArray.length; index++) {
    if (inputArray[index] > maxVal) {
      maxVal = inputArray[index];
    }
  }
  return maxVal;
}

console.log(findMaxValue([-10, 20, -5, -1]));

Understanding the Issue

At first glance, the function appears to work correctly by iterating through the array and updating maxVal whenever it encounters a larger number. However, there is a subtle bug: the initial value of maxVal is set to 0.

Why is this a problem? If all elements in inputArray are negative, maxVal will never be updated, and the function will incorrectly return 0, which is not even in the array!

For example, with the input [-10, 20, -5, -1], the function works fine because 20 is greater than 0, but if we change the input to [-10, -20, -5, -1], the function will incorrectly return 0 instead of -1.

Fixing the Bug

To ensure that maxVal correctly starts with the first element of the array, we should initialize it using the first element of inputArray instead of 0.

Corrected Code

function findMaxValue(inputArray) {
  if (inputArray.length === 0) return undefined; // Handle empty arrays
  let maxVal = inputArray[0];
  for (let index = 1; index < inputArray.length; index++) {
    // Start from index 1
    if (inputArray[index] > maxVal) {
      maxVal = inputArray[index];
    }
  }
  return maxVal;
}

console.log(findMaxValue([-10, 20, -5, -1])); // 20
console.log(findMaxValue([-10, -20, -5, -1])); // -1
console.log(findMaxValue([])); // undefined

Key Takeaways

• Always initialize variables with a value that makes sense for the given problem.
• When working with arrays, using the first element as an initial value is often safer.
• Consider edge cases like empty arrays or all-negative numbers when writing functions.
• Testing your function with multiple inputs helps catch hidden bugs.

By making this small yet crucial fix, we ensure our function works correctly for all cases. Happy coding!