Check if an element contains a specific css property.

hasCssProperty.js

// returns a boolean if the element contains that property
const hasCssProperty = (elmt, property) => {
  const elmtPropertyValue = window.getComputedStyle(elmt, null).getPropertyValue(property);
  return elmtPropertyValue ? true : false;
}

// live example
const elmt = document.querySelector('#video');

if (hasCssProperty(elmt, 'aspect-ratio')) {
  console.log('This browser supports aspect-ratio!');
} else {
  console.log('This browser does not support aspect-ratio!');
}