Detect changes in an attribute's value

observeAttribute.js

export function observeAttribute(element, attribute, callback) {
  const observer = new MutationObserver(mutations => {
    mutations
      .filter(x => x.type === 'attributes' && x.attributeName === attribute)
      .forEach(_ => callback(element.getAttribute(attribute)))
  })

  observer.observe(element, { attributes: true })

  return observer.disconnect
}