🔰iterable iterator

JS⟩ iteration ⟩ iterator ⟩ iterable iterator

an iterator that is itself iterable. (an iterator can easily be iterable by simply returning itself in its "make-iterator" method)

⭐️ 重點

iterators only iterate once❗️

iterable iterators：

• array.keys(), map.entries(), ...

• str.matchAll() - iterable iterator of all matches.

• s returned by generator function.

• iterator of all built-in iterable data types.

🔴 主題

• s are iterable iterators.

• make iterator iterable

• examples：

  • words in sentence - str.matchAll() returns an iterable iterator.

  • *list()

  • *integers()

🗺️ 圖解

💈範例

💾 replit：iterable iterator

let array = [1, 2, 3];                         // Array is iterable

// ⭐️ make an iterator
let iterator = array[Symbol.iterator]();

// first iteration result
let head = iterator.next();                    // { value: 1, done: false }

// ----------------------------
//     ⭐️ iterable iterator
// ----------------------------

// the iterator of a built-in iterable object is itself "iterable", i.e. it can:
// ⭐️ 1. spread itself into array elements or function arguments.
// ⭐️ 2. make an iterator for itself. (in fact, the iterator === itself)

// ⭐️ 1. spread itself into array elements
let tail = [...iterator];                      // [ 2, 3 ] ⭐️ 

// ⭐️ 2. make an iterator for itself
let it = iterator[Symbol.iterator]();

// ⭐️ 2. the iterator of the `iterator` is the `iterator` itself.
it === iterator;        // true❗

📘 手冊

• iterator protocol