// ⭐ %IteratorPrototype%
// -------------------------------------------------------
// prototype of all built-in iterators
//
// const IteratorPrototype = {
// [Symbol.iterator]() { return this },
// };
//
// Note:
// in ECMAScript spec, internal objects are enclosed
// in percent (%) signs.
// ⭐ %IteratorPrototype% is not directly accessible,
// but we can access it indirectly (from any built-in iterator).
//
// ⭐ array iterator -> ArrayIterator -> IteratorPrototype
const IteratorPrototype = Object.getPrototypeOf( // IteratorPrototype
Object.getPrototypeOf( // ArrayIterator
[][Symbol.iterator]() // ⭐ let empty array make an iterator
)
);
💈範例：
// what is the prototype of an array iterator?
let arrayIterator = [][Symbol.iterator]();
let proto = Object.getPrototypeOf(arrayIterator);
console.log(proto); // Object [Array Iterator] {}
;[
// `IteratorPrototype` is the prototype of ??? iterator ?
'abc'[Symbol.iterator](), // true (String iterator)
[].keys(), // true (iterator of Array keys)
new Map().entries(), // true (iterator of Map entries)
(function*() { })(), // true (generator: iterable iterator)
'aaa'.matchAll(/a/g), // true (iterator of all results)
].forEach(iterator => {
let ans = IteratorPrototype.isPrototypeOf(iterator);
console.log(ans);
});