Es6 provides "Set", it likes array but the data inside should be unqiue.
"Set" is a construct function, you should call:
var s = new Set();
Methods:
1. add(value)
[2,3,5,4,5,2,2].map(x =>s.add(x) ) for(num of s){ console.log(num); } //2, 3, 5, 4
2. delete(value)
[2,3,5,4,5,2,2].map(x =>s.add(x) ); s.delete("3"); for(num of s){ console.log(num); } //2, 5, 4
3. has(value)
[2,3,5,4,5,2,2].map(x =>s.add(x) ); s.delete("3"); for(num of s){ console.log(num); } s.has("3"); //false
4. size()
[2,3,5,4,5,2,2].map(x =>s.add(x) ) for(num of s){ console.log(num); } s.size(); // 4
5. claer()
[2,3,5,4,5,2,2].map(x =>s.add(x) ) for(num of s){ console.log(num); } s.clear(); s.size(); // 0
原文：http://www.cnblogs.com/Answer1215/p/4198106.html