Setting query string using Fetch GET request

I’m trying to use the new Fetch API:

I am making a GET request like this:

var request = new Request({
  url: 'http://myapi.com/orders',
  method: 'GET'
});
fetch(request);

However, I’m unsure how to add a query string to the GET request. Ideally, I want to be able to make a GET request to a URL like:

'http://myapi.com/orders?order_id=1'

In jQuery I could do this by passing {order_id: 1} as the data parameter of $.ajax(). Is there an equivalent way to do that with the new Fetch API?