another solution

nums.sort(function(a, b){return a-b});
let secLargest = nums[nums.length-2];
let largest = nums[nums.length-1];
for (let i = nums.length-1; i >= 0; i--){
if(nums[i-1] == nums[i]) {
    largest = nums[i-1];
    secLargest = nums[i-2];
} else {
    secLargest = nums[i-1];
    break;
}
}
return secLargest;

}