<button class="fab-button"></button>
<button class="fab-button" data-ripple="true"></button>
$(document).ready(function(){
$('.fab-button').addClass('[data-ripple="true"]');
});
const el = document.querySelector('.fab-button');
const key = 'ripple';
const val = 'true';
el.dataset[key] = val;
// или
el.setAttribute('data-' + key, val);
// или
el.outerHTML = el.outerHTML.replace('>', `data-${key}="${val}"$&`);
// или
const attr = document.createAttribute('data-'.concat(key));
attr.value = val;
el.attributes.setNamedItem(attr);