Find out duplicate numbers in an array without using JavaScript method ?

const numbers = [1,1,2,3,3,4,5,5,6,8,80,90,90,100];
const duplicateNumbers=[];

const duplicateNumbersList = (arr) => {
for(let i=0; i< arr.length; i++){
for(let j=i+1; j< arr.length; j++){
if(arr[i] === arr[j] && !duplicateNumbers.includes(arr[i])){
duplicateNumbers.push(arr[i]);
}
}
}
console.log(duplicateNumbers);
}

duplicateNumbersList(numbers);