var e={id:Math.random().toString(36).substr(2,11)};
var f={tx:[],rx:[]};

function TX(c=[],d=[]){
    f['tx'].push({"c":c,"d":d,"e":e});
    PARSE();
}

TX("init");

function SEND(){
    m=new XMLHttpRequest();
    m.open("POST","erv.php",true);
    m.timeout=5000;
    m.setRequestHeader("Content-type","application/json");
    m.onload=function(z){
	if(m.readyState===4 && m.status===200){
	    rx=JSON.parse(m.response);
	    f['rx']=f['rx'].concat(rx['d']);
	    e=rx['e'];
	    PARSE();
	}else{
	    alert("Ajax error: "+m.statusText);
	}
    }
    m.send(JSON.stringify(f['tx'][0]));
    f['tx'].shift();
}

function PARSE(){
    while(f['rx'].length){
	z=f['rx'][0];
	f['rx'].shift();
	switch(z['com']){
	    case "error":
		alert(z['txt']);
		break;
	}
    }
    if(f['tx'].length){
	SEND();
    }
}