How to import a ES2015 JavaScript module in an Ember.js project?

I want to use a JavaScript module (ES2015) in my Ember.js project, but it does not work.

I wrote a simple sample ES6 JavaScript file,

myES6lib.js

export default function square(b) {
  return b * b;
};

Following the MANAGEMENT DEPENDENCES, I ran

ember generate vendor-shim myES6lib

and added a line in ember-cli-build.js

app.import("vendor/shims/myES6lib.js");

then I called the square function in an Ember Controller

import MyES6lib from "myES6lib";
...
console.log("Square(5) = " + MyES6lib.square(5));

but I got an error message as follows:

Uncaught TypeError: _myES6lib.default.square is not a function

Any hints are appreciated, thanks in advance.

Note: I tried to transform myES6lib to ES5 code by Babel, but the result was same.