Question

I’m making a conversation system where 2 people can chat with each other. I’ve made an AJAX function which updates the DIV box containing the messages every 2 seconds.

This is working as intended, after a user have written a message. Why isn’t the AJAX call being run right away?

// SET AUTORUN updateMessages() EVERY 2 SECONDS
$(document).ready(function() {
    var interval
    window.onload = function(){
        interval = setInterval('updateMessages()', 2000);
    };
});

// UPDATE #mail_container_conversation
function updateMessages() {
    $.ajax({
        type: "POST",
        url: "<?php echo site_url(); ?>mail/ajaxupdate/<?php echo $user; ?>",
        data: dataString,
         
        success: function(data){
            $("#mail_container_conversation").html(data);
        }        
    });
}


// SEND NEW MESSAGE
$(function(){
    $("#mail_send").submit(function(){
        dataString = $("#mail_send").serialize();
         
        $.ajax({
        type: "POST",
        url: "<?php echo site_url(); ?>mail/send",
        data: dataString,
         
        success: function(data){
            updateMessages();
            $(".mail_conversation_answer_input").val('');
        }
                  
        });
                 
        return false;
    });
});

Answer 1

You should provide functions instead of strings to setTimeout/setInterval functions. And also there’s no need for you to set interval on window load event. You can just keep it as part of DOM ready:

$(function() {
    updateMessages(); // don't wait 2 seconds for first update
    setInterval(updateMessages, 2000); // update every 2 seconds
});

Everything else seems to should work as expected as long as your posback work when no data is being received (ref dataString).

I hope you do realise that you’re using implied globals and understand why that may be a big problem (ref dataString again).

How I would rewrite your code

I would rewrite your whole code into the following that removes implied global variable dataString, doesn’t pollute global scope with additional functions and uses setTimeout instead of interval which may in some cases be problematic (although in your case since it’ only runs every 2 seconds it shouldn’t be a problem if there’s no additional very complex client-side script execution)

I’ve kept everything within function closure local scope:

$(function() {

    var timeout = null;

    var form = $("#mail_send").submit(function(evt){
        evt.preventDefault();
        $(".mail_conversation_answer_input", form).val("");
        updateMessages();
    });

    var updateMessages = function() {

        // we don'w want submit to interfere with auto-updates
        clearTimeout(timeout);

        $.ajax({
            type: "POST",
            url: "<?php echo site_url(); ?>mail/send",
            data: form.serialize(),
            success: function(data){
                $("#mail_container_conversation").html(data);
                timeout = setTimeout(updateMessages, 2000);
            }
        });
    };

    // start updating
    updateMessages();

});

This code requires your server side (processing on /mail/send) to understand that when nothing is being posted (no data) that it doesn’t add empty line in the conversation but rather knows that this is just an update call. This functionality now uses only one server-side URL and not two of them. If you’d still require two, then this code should do the trick:

$(function() {

    var timeout = null;
    var url = {
        update: "<?php echo site_url();?>mail/ajaxupdate/<?php echo $user;?>",
        submit: "<?php echo site_url();?>mail/send",
        use: "update"
    };

    var form = $("#mail_send").submit(function(evt){
        evt.preventDefault();
        url.use = "submit";
        $(".mail_conversation_answer_input", form).val("");
        updateMessages();
    });

    var updateMessages = function() {

        // we don'w want submit to interfere with auto-updates
        clearTimeout(timeout);

        $.ajax({
            type: "POST",
            url: url[url.use],
            data: form.serialize(),
            success: function(data){
                $("#mail_container_conversation").html(data);
                url.use = "update";
                timeout = setTimeout(updateMessages, 2000);
            }
        });
    };

    // start updating
    updateMessages();

});