Remove duplicates from an array and return unique values in O(n) complexity

let arr = [1, 2, 3, 4, 3, 7, 6, 5, 4];

function unique(arr) {
    let items = {};
    arr.forEach((item) => {
        if (!items[item]) {
            items[item] = item;
        }
    });

    return items;
}

console.log(Object.values(unique(arr)));