Iterators ES6

Iterators_ES6.jsx

const arr = [1,2,3];

arr.map((i, item) => {
  console.log(item)
});

arr.forEach((item, i) => console.log(item, i))

for (let item of arr) {
  console.log(item);
}

for (let char of 'Hello') {
  console.log(char)
}

let types = new Set(['foo', 'tree', 'one']);

for(let type of types) {
  console.log(type);
}

let obj = {
  foo: 'bar',
  baz: 'aux'
};

for (let key of Object.keys(obj)) {
  console.log(key);
}

let iterator = {
  [Symbol.iterator]: function() {
    return this;
  },
  
  next: function() {
    return { value: 'hey', done: false } 
    // всегда возвращает это
  } 
}

const interator1 = iterator[Symbol.iterator]();

console.log( interator1.next() );


function createIterator(arr) {
  let index = 0;
  
  return {
    next: () => {
      return index < arr.length
        ? { value: arr[index++], done: false }
        : { done: true };
    }
  }
}

const myIterator = createIterator(['hey', 'yo', 'ya']);

console.log(myIterator.next())
console.log(myIterator.next())
console.log(myIterator.next())
console.log(myIterator.next())