Same code runs differently on different devices

Question

I'm new to coding, still learning. My friend gave me a task to write a function that does return the 2nd highest number from an array, I've managed to do it using array.prototype.sort(). He said to replace "-" with a "<" or ">" to make the code more clear, that's where the problem started.

I'm using VCS on windows, and it's not working properly. My friend uses a mac, everything works fine. Tried it on jsfiddle, everything works fine.

const secondMax = (arr) => {
  return arr.sort((a, b) => b - a)[1]; //does return the correct number after console.log()
};

const secondMax = (arr) => {
  return arr.sort((a, b) => a < b)[1]; //does not
};

"a < b" should be sorting descending "a > b" should be sorting ascending But no matter which operator I use, the sorting fails and just returns the second number from the array

Answer 1

You're supposed to return a number, not a boolean. So the first is correct. The latter might work by chance on some javascript engines, but it's not guaranteed to.

Answer 2

sort sorts the array as String by default. If you pass a comparator, then it's a function which will depend on two parameters and return :

• negative, if the first parameter is smaller than the second
• 0 if they are equal
• positive, if the first parameter is greater than the second

Using a logical operator instead of the above is mistaken.

However, if you are interested in finding the second largest number, then it's better to do it using a cycle:

var largestNumbers = [];
var firstIndex = (arr[0] < arr[1]) ? 1 : 0;
largestNumbers.push(arr[firstIndex]);
largestNumbers.push(arr[1 - firstIndex]);
for (var i = 2; i < arr.length; i++) {
    if (largestNumbers[1] < arr[i]) {
        if (largestNumbers[0] < arr[i]) {
            largestNumbers[1] = largestNumbers[0];
            largestNumbers[0] = arr[i];
        }
    }
}

This is quicker than sorting an array and more importantly, it does not destroy your initial order just to find the second largest number.