Must websockets have heartbeats?

Question

When I read about websockets, heartbeats are usually mentioned as a must have. MDN even writes about a special opcode for heartbeats.

But are heartbeats a mandatory part

Answer 1

It is mandatory or not depending on client and server implementations. If you are connected to a server that requires you to answer the PING with a PONG, you will be probably disconnected in case you don't reply. Same if you are the server and a client is sending you PING.

Server and client implementations vary (there are a myriad of them), but the browser´s javascript client do not send PING, and do not provide any API to do so, although It replies to PINGs with PONGs.