a.js

// object literal. Very flexible and with shorthand notation for methods, it's very nice.
const obj = {
   addTodo() {
   },
   removeTodo() {
   },
   transactions: { // sub object
      fetchTodos() {
      }
   }
}
// ES6 (without drafts)
class ToDo {
    // I don't want to do this because it's draft. 
   // static transactions = {
   //   fetchTodos() {}
   //}
   addTodo() {
   }
   removeTodo() {
   }
}
// so old way
ToDo.prototype.transactions = { 
  fetchTodos() {
  }
}