SOURCE

let set = new Set([1,1,3,4,5]);
set.forEach(function(value,key,ownerSet) {
    // console.log(value)
    // console.log(key)
    // console.log(ownerSet)
})
console.log(+0 == -0)
console.log(Object.is(+0 == -0))
console.log(set)
// console.log(Object.is(set[0],set[2]));
let wset = new WeakSet();
// let key = {};   
wset.add({},{});
console.log(wset.size)