ShadowRoot.mode

var mode = shadowRoot.mode

  // We create a closed shadow root, that is not accessible
  let element = document.createElement("div");
  element.attachShadow({ mode: "closed" });
  element.shadowRoot // null as the shadow root is closed

  // We create an open shadow root, that is accessible
  let element2 = document.createElement("div");
  element2.attachShadow({ mode: "open" });
  console.log("The shadow is" + element2.shadowRoot.mode) // logs "The shadow is open"
  element2.shadowRoot.innerHTML("

Opened shadow

") // The shadow is open, we can access it from outside