let arr = [],
elements = 10;
for (let i = 0; i < elements; i += 1) {
arr.push("X");
}
for (let i = 0; i < elements; i++) {
let index = Math.round(Math.random() * (arr.length));
arr.splice(index, 1, i.toString());
}
console.log(arr);
/*
run:
["X", "0", "4", "5", "X", "7", "X", "3", "6", "9", "8"]
*/