How to control the execution of Javascript

Question

I wants to get the last id from MySQL table and create a cookie with this value in Javascript and PHP. following is my code.

if (getCookie("id")=='') {
    last_visitor_id = get_last_visitor();
    deviceID = last_visitor_id++;
    setCookie("id", deviceID , 365);
    $.ajax({
        url:"save_device.php?deviceID="+deviceID+
            "&websiteID="+WebsiteID+
            "&width="+sWidth+
            "&height="+sHeight,
            success:function (datasource) {
                // alert (datasource);
            }
        }
    );  
} else {
    deviceID = getCookie("id");
    alert ("working...." + deviceID);
}


 function get_last_visitor(){
    $.ajax({url:"get_last_visitor.php",success:function(last_visitor){
         // last_visitor++;
         //alert ("Last Visitor ID " + last_visitor);
         return (last_visitor);
    }});

}

There is a problem with code. Before it gets the last visitor id it executes the setCookie function even though there is no value returned by the get_last_visitor() function. Functions return the value after some time, but in the mean time it creates a cookie with NAN.

Can any one suggest some solution?

http://stackoverflow.com/questions/6847697/how-to-return-value-from-an-asynchronous-callback-function ? — parchment, Aug 19 '14 at 12:22

Claudio Redi · Answer 1 · 2014-08-19T12:31:29.403

2

It make no sense to execute return (last_visitor) from your ajax call since it is async. The execution flow is not waiting for the ajax call to finish, next line is executed inmetiatly so get_last_visitor is returning null ALWAYS.

You can change your code like this to use the success ajax callback to execute your logic

if (getCookie("id")==''){
    $.ajax({url:"get_last_visitor.php"})
    .done(function(last_visitor_id) {
        deviceID = last_visitor_id++;
        setCookie("id", deviceID , 365);
        $.ajax({url:"save_device.php?deviceID="+deviceID+"&websiteID="+WebsiteID+"&width="+sWidth+"&height="+sHeight,success:function(datasource){
            // alert (datasource);
        }});    
    });
} else {
    deviceID = getCookie("id");
    alert ("working...." + deviceID);
}

edited Aug 19 '14 at 12:31

answered Aug 19 '14 at 12:22

Claudio Redi

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your are right, it always returning null value. can you please suggest some solution ???? – user2674341 Aug 19 '14 at 12:24
i can see the returned value in firebug, but its not proceeding to the next line. i mean its still not creating the cookie. – user2674341 Aug 19 '14 at 12:45
i am getting this error: TypeError: $.ajax(...).done is not a function – user2674341 Aug 19 '14 at 13:32
@user2674341: what jquery version are you using? – Claudio Redi Aug 19 '14 at 14:00

How to control the execution of Javascript

1 Answers1