🔰iteration

JS ⟩ iteration

three types that are related to iteration：

• iterable - object that can make iterators to loop over itself.

• iterator - object that can produce the next iteration result.

• iteration result - object that holds the result of each step of the iteration.

🔴 主題

• custom extension

  • Iterable+ext

• loop statements for iterations

  • for / for-in / for-of / for-await

  • while, do...while

• iterable

  • make-iterator method

  • only-iterate-once iterable

  • make iterables

  • make iterator iterable

  • iterable examples

• iterator

  • next() - iterators must implement next() method.

  • make-iterator method of an iterable - iterables can make iterators.

  • iterators only iterate once❗️ - iterators only iterate once.

  • iterable iterator - an iterator that is itself iterable.

  • make iterator iterable

  • IteratorPrototype - prototype of all built-in iterators.

  • Iterator - extension for (built-in) iterators.

• iteration result

• iteration

  • three types that are related to the iteration.

    • iterable - object that can be iterated.

    • iterator - object that performs the iteration.

    • iteration result - object that holds the result of each step of the iteration.

  • Generator - objects returned by generator function.

  • generator function - return .

  • generator examples

⭐️ 重點

to iterate an iterable object (the hard way)：

1. call iterable object's iterator method to get an iterator.

2. call the iterator's next() method repeatedly until the iteration result is done.

🗺️ 圖解

💈範例

💾 replit：iterator

let iterable = [1, 2, 3];

// ⭐️ iterate an iterable "the hard way"
let iterator = iterable[Symbol.iterator]();  // ⭐️ 1. make an iterator
let result = iterator.next();                // ⭐️ 2. first result

while (!result.done) {
    console.log(result.value);
    result = iterator.next();                // call next() repeatedly
}

// ⭐️ the easy way
for (const i of iterable) { console.log(i) } // 1, 2, 3

📘 手冊

• Statements and declarations ⟩ iterations

• Iterators and generators

  • iterable protocol

  • Generator

• Loops and iteration

  • for...of

• Symbol.iterator ( = makeIterator in Swift )

📗 參考

• ExploringJS ⟩ 21. Iterables and Iterators ⭐️

• JavaScript: The Definitive Guide ⟩ 12. Iterators and Generators

• JS.info ⟩

  • iterables

  • Generators

• 2ality ⟩ JavaScript needs more helper functions for iteration (map, filter, etc.)

• 認識 JavaScript Iterable 和 Iterator