const arr = [1, 6, 43, 3, 56, 0, 9, 98];
function composeNewArray(arr, l) {
const newArr = [];
for (let i=0;i<l;i++) {
while(1) {
let index = Math.floor(Math.random() * (arr.length - 1));
if (newArr.indexOf(arr[index])!== -1) {
continue;
} else {
newArr.push(arr[index]);
break;
}
}
}
return newArr;
}
const newArr = composeNewArray(arr, 4);
console.log(newArr);