Uncaught TypeError: Cannot read property 'listeners' of undefined

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We've implemented LiveDJ function in IceCast and there is three mount points now, previously there was only one. JSON structure has changed as a result of that. We need to parse this information from active mountpoint: title and listeners number.

I'm trying to determine the active mountpoint using 'if' statement, but I can't find a solution how to avoid this error in browser: "Uncaught TypeError: Cannot read property 'listeners' of undefined". It stops the script.

How could I check if my variable is 'undefined' so I could continue my logic? Note: I get this undefined only when server is started freshly and Live session was not established yet. If I connect and disconnet a live stream, JSON structure changes and I get all variables defined then.

<script>
function radioTitle() {
                 $.ajax({
                    url: "http://ift.tt/18sEpsj",
                    dataType: "text",
                    success: function(data) {
                        var json = $.parseJSON(data);           
                                                
                                                var listeners = json.icestats.source.listeners;
                                                var listenersLive = json.icestats.source[0].listeners; // Error in browser "Uncaught TypeError: Cannot read property 'listeners' of undefined"
                                                var listenersDJ = json.icestats.source[1].listeners;
                                                
                                                if(listeners > listenersDJ) {
                                                //Fresh start
                                                }
                                                else if(listenersDJ > listenersLive) {
                                                //autoDJ
                                                } 
                                                else {
                                                //Live
                                                }
                    }
                }); 
                                }
$(document).ready(function () {
setTimeout(function () {radioTitle();}, 0);
setInterval(function () {radioTitle();}, 15000); 
});
 </script>

asked 1 min ago

user3647341

1

Uncaught TypeError: Cannot read property 'listeners' of undefined