Stop setInterval

You need to set the return value of setInterval to a variable within the scope of the click handler, then use clearInterval() like this:

var interval = null;$(document).on('ready',function(){    interval = setInterval(updateDiv,3000);});function updateDiv(){    $.ajax({        url: 'getContent.php',        success: function(data){            $('.square').html(data);        },        error: function(){            clearInterval(interval); // stop the interval            $.playSound('oneday.wav');            $('.square').html('<span style="color:red">Connection problems</span>');        }    });}

Use a variable and call clearInterval to stop it.

var interval;$(document).on('ready',function()  interval = setInterval(updateDiv,3000);  });  function updateDiv(){    $.ajax({      url: 'getContent.php',      success: function(data){        $('.square').html(data);      },      error: function(){        $.playSound('oneday.wav');        $('.square').html('<span style="color:red">Connection problems</span>');        // I want to stop it here        clearInterval(interval);      }    });  }

You have to assign the returned value of the setInterval function to a variable

var interval;$(document).on('ready',function(){    interval = setInterval(updateDiv,3000);});

and then use clearInterval(interval) to clear it again.