03_ugly_form_checkbox.js

function materializeCheckboxes() {
    var parentEl;
    document.querySelectorAll('input[type="checkbox"]').forEach(function(control) {
        parentEl = control.parentElement;
        control.classList.add('mdl-checkbox__input');
        if (parentEl.tagName == "LABEL") {
            parentEl.setAttribute('for', control.id || control.name)
            parentEl.classList.add('mdl-checkbox', 'mdl-js-checkbox', 'mdl-js-ripple-effect');
        }
    });
}

function materializeControls() {
    materializeTextInputs();
    materializeSelects();
    materializeRadioButtons();
    materializeCheckboxes();
}