/**
 * @param {number[]} arr
 * @return {boolean}
 */
var uniqueOccurrences = function(arr) {
     const hashmap = {};

    for (let i = 0; i < arr.length; i++) {
        const item = arr[i];
        if (hashmap[item]) {
            hashmap[item] = hashmap[item] + 1;
        } else {
            hashmap[item] = 1;
        }
    }

    const values = Object.values(hashmap);
    const set = new Set(values);
    return set.size === values.length;
};