You can try ES6 Modules in Google Chrome Beta (61) / Chrome Canary.
Reference Implementation of ToDo MVC by Paul Irish - https://paulirish.github.io/es-modules-todomvc/
I've basic demo -
//app.js
import {sum} from './calc.js'
console.log(sum(2,3));
//calc.js
let sum = (a,b) => { return a + b; }
export {sum};
<html>
<head>
<meta charset="utf-8" />
</head>
<body>
<h1>ES6</h1>
<script src="app.js" type="module"></script>
</body>
</html>
Hope it helps!