Create GUID UUID in JavaScript

function guid() {
  function s4() {
    return Math.floor((1 + Math.random()) * 0x10000)
      .toString(16)
      .substring(1);
  }
  return s4() + s4() + '-' + s4() + '-' + s4() + '-' +
    s4() + '-' + s4() + s4() + s4();
}

or

function S4() {
    return (((1+Math.random())*0x10000)|0).toString(16).substring(1); 
}
 
// then to call it, plus stitch in '4' in the third group
guid = (S4() + S4() + "-" + S4() + "-4" + S4().substr(0,3) + "-" + S4() + "-" + S4() + S4() + S4()).toLowerCase();
console.log(guid);