ES6 module, import, export equivalent code to achieve browser compatible

init.js

// init function, just a test
function init() {
    $(".accordion").on("click", ".accordion-header", function() {
        $(this).toggleClass("active").next().slideToggle();
    });
    return true;
}

// run it when it;s ready
$(document).ready(init);

// browser compatible module export
if (typeof module !== 'undefined' &&
    typeof module.exports !== 'underfined'){
    module.exports= init;
}else{
    if (typeof define === 'function' && define.amd){
        define([], function(){ return init;});
    }else
        window.init = init;
}

init.test.js

// use require instead of import
const init = require('./init.js');

test('Init() Test', ()=> {
    expect(init()).toBe(true);
}
);