Exiting a callback function

I would like to ask how to exit the callback function given below before ajax call if valueid2 equals 0

callback: function() {
                        console.log('save');
                        console.log($('#re_confirm')[0].checked);
                        var valueid = document.getElementById('idtable').value
                        if(valueid == 0)
                           myFunction();
                        var valueid2 = document.getElementById('idtable').value

                         $.ajax({
                            url : "<?php echo base_url(); ?>index.php/home/update_booking",
                            type: "post",
                            data: {
                                "table_id" : $('#idtable').val(),
                            },
                            success: function(response){
                                   ...
                            }
                       });
      }

Please tell me how to exit the callback function.

You can do it by simply using return. This will return the function if valueid2 is 0, and the ajax call will not be run:

callback: function() {
    console.log('save');
    console.log($('#re_confirm')[0].checked);
    var valueid = document.getElementById('idtable').value
    if(valueid == 0)
        myFunction();
    var valueid2 = document.getElementById('idtable').value

    if (valueid2 == 0) {
        return; // This return here will end the function
    }

    $.ajax({
    url : "<?php echo base_url(); ?>index.php/home/update_booking",
    type: "post",
    data: {
        "table_id" : $('#idtable').val(),
    },
    success: function(response){
        ...
    }
    });
}