The part property of the Element interface represents the part identifier(s) of the element (i.e. set using the part attribute), returned as a DOMTokenList. These can be used to style parts of a shadow DOM, via the ::part pseudo-element.

A DOMTokenList object.

The following excerpt is from our shadow-part example. Here the part attribute is used to find the shadow parts, and the part property is then used to change the part identifiers of each tab so the correct styling is applied to the active tab when tabs are clicked.

const tabs = [];
const children = this.shadowRoot.children;

for (const elem of children) {
  if (elem.getAttribute("part")) {
    tabs.push(elem);
  }
}

tabs.forEach((tab) => {
  tab.addEventListener("click", (e) => {
    tabs.forEach((tab) => {
      tab.part = "tab";
    });
    e.target.part = "tab active";
  });

  console.log(tab.part);
});

• ::part
• part