string.@@iterator

string[Symbol.iterator]

var string = 'A\uD835\uDC68';

var strIter = string[Symbol.iterator]();

console.log(strIter.next().value); // "A"
console.log(strIter.next().value); // "\uD835\uDC68"

var string = 'A\uD835\uDC68B\uD835\uDC69C\uD835\uDC6A';

for (var v of string) {
  console.log(v);
}
// "A"
// "\uD835\uDC68"
// "B"
// "\uD835\uDC69"
// "C"
// "\uD835\uDC6A"