Edit in JSFiddle

var mySet = new Set();
console.log([...mySet]);

mySet.add(1); // Set [ 1 ]
console.log([...mySet]);

mySet.add(5); // Set [ 1, 5 ]
console.log([...mySet]);

mySet.add(5); // Set [ 1, 5 ]
console.log([...mySet]);

mySet.add('some text'); // Set [ 1, 5, 'some text' ]
console.log([...mySet]);

var o = {a: 1, b: 2};
mySet.add(o); // Set [ 1, 5, 'some text', { a: 1, b: 2 } ]
console.log([...mySet]);