SOURCE

const a = [1,1,2,2,2,3,4,5,6]
function distinct(arr) {
    let re = [];
    let pushed = [];
    for(let i of arr){
        if(!pushed.includes(i)){
            re.push(i);
            pushed.push(i);
        }
    }
    return re;
}
let b = distinct(a);
console.log(b)