js 如何生成uuid

/**
 * 生成UUID
 */
function generateUUID() {
  let d = new Date().getTime();
  let uuid = 'xxxxxxxxxxxx4xxxyxxxxxxxxxxxxxxx'.replace(/[xy]/g, function (c) {
    // let uuid = 'xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx'.replace(/[xy]/g, function(c) {
    let r = (d + Math.random() * 16) % 16 | 0;
    d = Math.floor(d / 16);
    return (c == 'x' ? r : (r & 0x3) | 0x8).toString(16);
  });
  return uuid;
}