DataTransferItem: метод getAsString()

getAsString(callbackFn)

function dropHandler(ev) {
  console.log("Drop");
  ev.preventDefault();
  const data = ev.dataTransfer.items;
  for (let i = 0; i < data.length; i += 1) {
    if (data[i].kind === "string" && data[i].type.match("^text/plain")) {
      // This item is the target node
      data[i].getAsString((s) => {
        ev.target.appendChild(document.getElementById(s));
      });
    } else if (data[i].kind === "string" && data[i].type.match("^text/html")) {
      // Drag data item is HTML
      console.log("… Drop: HTML");
    } else if (
      data[i].kind === "string" &&
      data[i].type.match("^text/uri-list")
    ) {
      // Drag data item is URI
      console.log("… Drop: URI");
    } else if (data[i].kind === "file" && data[i].type.match("^image/")) {
      // Drag data item is an image file
      const f = data[i].getAsFile();
      console.log("… Drop: File");
    }
  }
}