Iterators and generators - JavaScript | MDN - Mozilla
An object is iterable if it defines its iteration behavior, such as what values are looped over in a for...of construct. Some built-in types, such as Array or Map, have a default iteration behavior, while other types (such as Object) do not.. In order to be iterable, an object must implement the @@iterator method. This means that the object (or one of the objects up its prototype chain) must ...