MediaQueryList.matches

The matches read-only property of the MediaQueryList interface is a boolean value that returns true if the document currently matches the media query list, or false if not.

You can be notified when the value of matches changes by watching for the change event to be fired at the MediaQueryList.

const mql = window.matchMedia("(orientation:landscape)");
mql.addEventListener("change", (event) => {
  if (event.matches) {
    console.log("Now in landscape orientation");
  } else {
    console.log("Now in portrait orientation");
  }
});