SOURCE

var origin = [1, 2, 'a', 3, 1, 'b', 'a'];
var result = new Set();
var repeat = new Set();
origin.forEach(item => {
    result.has(item) ? repeat.add(item) : result.add(item);
})
console.log(result); // {1, 2, "a", 3, "b"}
console.log(repeat); // {1, "a"}