How do I convert this jquery to pure javascript?

Hello I want to convert the following to pure JS if possible.

My ultimate goal is to display the var "bar" if checkboxes with id's ("checkbox1", "checkbox2", "checkbox3") are selected + display corresponding id's ("item1", "item2", "item3").

$('input:checkbox').change(function () {
    if ($(this).is(':checked')) {
        switch (this.id){
            case 'checkbox1':
                bar.show();
                item1.show();
                break;
            case 'checkbox2':
                bar.show();
                item2.show();
                break;
            case 'checkbox3':
                bar.show();
                item3.show();
                break;
            default:
                bar.hide();
        }
    } else {
        bar.hide();
    }
});

How can i simply do this?