makeGood.js

var makeGood = function(s) {
    // Create a stack to keep of the characters
    let stack = [];

    // Iterate over each character in the string
    for (let i = 0; i < s.length; i++) {
        // If the stack is not empty and the current character is the opposite case of the last character in the stack
        if (stack.length > 0 && Math.abs(s.charCodeAt(i) - stack[stack.length - 1].charCodeAt(0)) === 32) {
            // Remove the last character from the stack
            stack.pop();
        } else {
            // Otherwise, add the current character to the stack
            stack.push(s[i]);
        }
    }

    // Join the remaining characters in the stack into a string and return it
    return stack.join('');
};