let arr = [11, 11, 2, 2, 5, 5, 5, 5, 3];
// Create a map, put every number and its corresponding number
let countObj = {};
for (i = 0; i <= arr.length - 1; i++) {
let v = arr[i];
if (countObj[v]) {
countObj [i] ++;
} else {
countObj [i] = 1;
}
}
// console.log(countObj); //{ '2': 2, '3': 1, '5': 4, '11': 2 }
for (let key in countObj) {
if (countObj [key] === 1) {// is determined to occur in 1 in which the object attributes
console.log(key);//3...
}
}