Singleton is a design pattern used to limit the number of a class instances to one (or may be more)
and restricting any user wants a new object to use the already constructed object eliminating multiple copies of the same object
A socket is a software endpoint that establishes bidirectional communication between a server program and one or more client programs.
It has two types UDP and TCP
It’s a connectionless protocol.
It doesn’t required initializing a connection before doing communication.
there is no guarantee that the datagrams you have sent will be received in the same order by the receiving socket. You can’t know also if it’s received without defects or if it reached its destination
It’s a connection-oriented protocol.
a connection must first be established between the pair of sockets. While one of the sockets listens for a connection request (server), the other asks for a connection (client).
It is guaranteed that the packets you send will be received in the order in which they were sent.
the default way to use the ajax feature is to make an instance from the XMLHttpRequest Object through this simplified statement
request = new XMLHttpRequest();
unfortunately older versions of Internet Explorer doesn’t have a native XMLHTTPRequest Object, but we can get one by getting it from an ActiveXObject