Refactoring JavaScript: Separation of Concerns - Styles on JS (Fixed)

style-modifying-fixed-by-toggling.js

function toggleFooHasError() {
    let foo = document.getElementById('foo');
    if (foo.classList.contains('has-error')) {
        foo.classList.remove('has-error');
    } else {
        foo.classList.add('has-error');
    }
}

toggleFooHasError();
// all styling must be done in css, just assign a class to it