Spread operator and iterators in JavaScript

The spread operator expands any object that has an iterator. This will take the default iterator. Let's look at an example. Let we have the following Map collection:

javascriptlet map = new Map();
map.set('a', 1);
map.set('b', 2);
map.set('c', 3);

By default, when decomposed, a two-dimensional array will be obtained:

javascriptlet arr = [...map];
console.log(arr); // [['a', 1], ['b', 2], ['c', 3]]

To obtain an array of keys, we decompose the corresponding iterator:

javascriptlet arr = [...map.keys()];
console.log(arr); // ['a', 'b', 'c']

Let's do the same to get an array of values:

javascriptlet arr = [...map.values()];
console.log(arr); // [1, 2, 3]

javascriptlet obj = {
  a: 1,
  b: 2,
  c: 3,
  [Symbol.iterator]: function *(){
    for (let key in this){
      yield this[key];
    }
  }
};