for... of

for ... of 문은 반복 가능한 객체 (내장 String, Array, 예를 들어 Array와 유사한 인수 또는 NodeList 객체, TypedArray, Map 및 Set 및 user-defined iterables 포함)를 반복하는 루프를 만들고,

객체의 각 고유한 속성값에 대해 실행될 명령문을 사용하여 custom 반복 후크를 호출합니다.

for (variable of iterable) {
  statement
}

Iterating over an Array

let iterable = [10, 20, 30];

for (let value of iterable) {
  value += 1;
  console.log(value);
}
// 11
// 21
// 31

You can use const instead of let too, if you don't reassign the variable inside the block.let iterable = [10, 20, 30];

for (const value of iterable) {
  console.log(value);
}
// 10
// 20
// 30

Iterating over a String

let iterable = 'boo';

for (let value of iterable) {
  console.log(value);
}
// "b"
// "o"
// "o"

Iterating over a TypedArray

let iterable = new Uint8Array([0x00, 0xff]);

for (let value of iterable) {
  console.log(value);
}
// 0
// 255

Iterating over a Map

let iterable = new Map([['a', 1], ['b', 2], ['c', 3]]);

for (let entry of iterable) {
  console.log(entry);
}
// ['a', 1]
// ['b', 2]
// ['c', 3]

for (let [key, value] of iterable) {
  console.log(value);
}
// 1
// 2
// 3

Iterating over a Set

let iterable = new Set([1, 1, 2, 2, 3, 3]);

for (let value of iterable) {
  console.log(value);
}
// 1
// 2
// 3

Iterating over the arguments object

(function() {
  for (let argument of arguments) {
    console.log(argument);
  }
})(1, 2, 3);

// 1
// 2
// 3

Iterating over a DOM collection

Iterating over DOM collections like NodeList : the following example adds a read class to paragraphs that are direct descendants of an article:

// Note: This will only work in platforms that have
// implemented NodeList.prototype[Symbol.iterator]
let articleParagraphs = document.querySelectorAll('article > p');

for (let paragraph of articleParagraphs) {
  paragraph.classList.add('read');
}

Closing iterators

In for...of loops, abrupt iteration termination can be caused by break , continue , throw or return . In these cases, the iterator is closed.

function* foo(){ 
  yield 1; 
  yield 2; 
  yield 3; 
}; 

for (let o of foo()) { 
  console.log(o); 
  break; // closes iterator, triggers return
}

Iterating over generators

function* fibonacci() { // a generator function
  let [prev, curr] = [0, 1];
  while (true) {
    [prev, curr] = [curr, prev + curr];
    yield curr;
  }
}

for (let n of fibonacci()) {
  console.log(n);
  // truncate the sequence at 1000
  if (n >= 1000) {
    break;
  }
}

Iterating over other iterable objects

You can also iterate over an object that explicitly implements iterable protocol:

var iterable = {
  [Symbol.iterator]() {
    return {
      i: 0,
      next() {
        if (this.i < 3) {
          return { value: this.i++, done: false };
        }
        return { value: undefined, done: true };
      }
    };
  }
};

for (var value of iterable) {
  console.log(value);
}
// 0
// 1
// 2