how to create uuid in javascript

1function uuid(){
2    var dt = new Date().getTime();
3    var uuid = 'xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx'.replace(/[xy]/g, function(c) {
4        var r = (dt + Math.random()*16)%16 | 0;
5        dt = Math.floor(dt/16);
6        return (c=='x' ? r :(r&0x3|0x8)).toString(16);
7    });
8    return uuid;
9}
10
11

1function uuid() {
2  return 'xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx'.replace(/[xy]/g, function(c) {
3    var r = Math.random() * 16 | 0, v = c == 'x' ? r : (r & 0x3 | 0x8);
4    return v.toString(16);
5  });
6}
7
8var userID=uuid();//something like: "ec0c22fa-f909-48da-92cb-db17ecdb91c5" 

1  uuidv4() {
2    return 'xxxxxxxxxxxxxxxxxxxxxxxxxxxx'.replace(/[xy]/g, (c) => {
3      var r = (Math.random() * 16) | 0,
4        v = c == 'x' ? r : (r & 0x3) | 0x8;
5      return v.toString(16);
6    });
7  }