object.with.generator.js

const objWithIterator = { 
  [Symbol.iterator]() {
      return {
          next: function() {
            console.log('do next');
            return {done: false, value: 'foo'}; 
          },
          return: function() {
            console.log('do return');
            return {done: true, value: 'foo'}; 
          },
          throw: function() {
            console.log('do throw');
            throw new Error('foo'); 
          }
      };
   }
}

objWithIterator[Symbol.iterator]().next();
// do next
// {done: false, value: "foo"}