@nguyenmv2/buy-button/src/utils/element-class.js

BuyButton.js allows merchants to build Shopify interfaces into any website

export function addClassToElement(className, element) {
  if (!className) {
    return;
  }
  if (element.classList) {
    element.classList.add(className);
  } else {
    const classes = element.className.split(' ');
    if (classes.indexOf(className) > -1) {
      return;
    }
    element.setAttribute('class', `${element.className} ${className}`);
  }
}

export function removeClassFromElement(className, element) {
  if (!className) {
    return;
  }
  if (element.classList) {
    element.classList.remove(className);
  } else {
    element.setAttribute('class', element.className.replace(className, ''));
  }
}