JavaScript ES6: Grouping methods in es6 classes?

A few of us are trying to create a JavaScript library to quickly run JSON queries on a RESTful API.

What I'd like to do is group a set of methods relative to their purpose.

For example;

Through the API I am able to get user attributes. Instead of having all of these methods under the main object, I'd like to group them within the API class object.

i.e. Transform this:

myAPI.getUserById()

To This:

myAPI.User.getByID()

myAPI.User.getByName()

We'll use the code below as a simple example. How might I have my User methods nested within a User Object within myAPI Class??

class myAPI {
  constructor(url) {
    this.url = url;

    //Code to connect to instance...

  }

  getUserById(userId){
    // function
  }
}

Solved

class myAPI {
  constructor(url) {
    this.url = url;
    this.UserAPI = new UserClass(this);

    //Code to connect to instance...

  }

  getUserById(userId){
    // function
  }
}

class UserClass {
  constructor(parent){
    this.myAPI = parent;
  }
}