Edit in JSFiddle

console.clear();

function isUniqueQuadratic(arr) {
  for (let i = 0; i < arr.length; i++) {
    for (let j = 0; j < arr.length; j++) {
      if (i !== j && arr[i] === arr[j]) {
        return false;
      }
    }
  }
  return true;
}

let smallDuplicate = [1, 4, 6, 10, 4];
let largeDuplicate = _.range(3500).concat(5).concat(_.range(10000, 3510));

let smallUnique = [1, 4, 5, 10, 52];
let largeUnique = _.range(10000);

console.log(isUniqueQuadratic(smallDuplicate))
console.log(isUniqueQuadratic(largeDuplicate))
console.log(isUniqueQuadratic(smallUnique))
console.log(isUniqueQuadratic(largeUnique))