You cannot declare function declaration using ES6 arrow function. Arrow functions are meant to be replacement for traditional function expressions.
// traditional function expression
var foo = function () {
return 'foo';
};
// ES6 arrow function
var foo = () => ({}); // single line must be surrounded with parenthesis
var bar = () => 'bar'; // single line do not need return keyword
var baz = () => {
return 'baz'; // multiline needs explicit return keyword
};
In order to better understand the functions I would highly recommend this article https://kangax.github.io/nfe/