Detailed explanation of JS WebSocket disconnection reasons and heartbeat mechanism

ws.onclose = function (e) {
  console.log('websocket disconnected: ' + e.code + ' ' + e.reason + ' ' + e.wasClean)
  console.log(e)
}

var lockReconnect = false; //Avoid repeated ws connections var ws = null; //Determine whether the current browser supports WebSocket
var wsUrl = serverConfig.socketUrl;
createWebSocket(wsUrl); //Connect to ws

function createWebSocket(url) {
    try{
        if('WebSocket' in window){
            ws = new WebSocket(url);
        }
        initEventHandle();
    }catch(e){
        reconnect(url);
        console.log(e);
    }     
}

function initEventHandle() {
    ws.onclose = function () {
        reconnect(wsUrl);
        console.log("llws connection closed!"+new Date().toLocaleString());
    };
    ws.onerror = function () {
        reconnect(wsUrl);
        console.log("llws connection error!");
    };
    ws.onopen = function () {
        heartCheck.reset().start(); //Heartbeat detection reset console.log("llws connection successful!"+new Date().toLocaleString());
    };
    ws.onmessage = function (event) { //If a message is received, the heartbeat detection is reset heartCheck.reset().start(); //Getting any message means that the current connection is normal console.log("llws received the message:" + event.data);
        if(event.data!='pong'){
            let data = jsON.parse(event.data);
        }
    };
}
// Listen for window closing events. When the window is closed, actively close the websocket connection to prevent the server from throwing an exception when the window is closed before the connection is disconnected.
window.onbeforeunload = function() {
    ws.close();
}  

function reconnect(url) {
    if(lockReconnect) return;
    lockReconnect = true;
    setTimeout(function () { //If it fails to connect, it will keep reconnecting. Set a delay to avoid too many requests createWebSocket(url);
        lockReconnect = false;
    }, 2000);
}

//Heartbeat detection var heartCheck = {
    timeout: 1000, //Send a heartbeat every minute timeoutObj: null,
    serverTimeoutObj: null,
    reset: function(){
        clearTimeout(this.timeoutObj);
        clearTimeout(this.serverTimeoutObj);
        return this;
    },
    start: function(){
        var self = this;
        this.timeoutObj = setTimeout(function(){
            //Here a heartbeat is sent, and after the backend receives it, a heartbeat message is returned.
            //onmessage gets the returned heartbeat, which means the connection is normalws.send("ping");
            console.log("ping!")
            self.serverTimeoutObj = setTimeout(function(){//If it is not reset after a certain period of time, it means that the backend has actively disconnected ws.close(); //If onclose will execute reconnect, we just need to execute ws.close(). If reconnect is executed directly, onclose will be triggered, resulting in two reconnections}, self.timeout)
        }, this.timeout)
    }
}
    //Method called after receiving client message @OnMessage  
    public void onMessage(String message, Session session) {  
        if (message.equals("ping")) {
        }else{
        . . . .
        }
   }