help me to reduce the amount of code in a jquery script

Currently I'm using this jquery script combining with php (doesn't matter):

<script type="text/javascript" charset="utf-8">
$(document).ready(function(){
    var select      = "<?php if_exist($select,      '');   ?>";
    var event       = "<?php if_exist($event,       'click');   ?>";
    var display     = "<?php if_exist($display, '#display');  ?>";
    var loading     = "<?php if_exist($loading, '#loading');  ?>";
    var datatype    = "<?php if_exist($datatype,    'json'); ?>";
    var cache;
    if (event == "submit"){ $("input:submit").hide(); }
    $(select).bind( event , function(key){
        if ( event == "keypress" ) {
            if ( key.which == <?php if_exist($keycode, '13'); ?> ) {
                $(loading).show();
                $.post(
                    $(select).attr("action"),
                    $(select).serialize(),
                    function(data){
                        if (datatype == "html" || datatype == "text"){ var returned = data; }
                        if (datatype == "json"){ var returned = data<?php if_exist($return, '.return'); ?>; }
                        if (returned != cache)
                        {
                            cache = returned;
                            if (datatype == "html" || datatype == "text"){ $(display).hide().html(data).fadeIn(); }
                            if (datatype == "json"){ $(display).hide().autoRender(data).fadeIn(); }
                            $(loading).hide();
                        }
                    },
                    datatype
                );
                return false;
            };
        }
        else
        {
            $.post(
                $(select).attr("action"),
                $(select).serialize(),
                function(data){
                    if (datatype == "html" || datatype == "text"){ var returned = data; }
                    if (datatype == "json"){ var returned = data<?php if_exist($return, '.returnValue'); ?>; }
                    if (returned != cache)
      开发者_运维知识库              {
                        cache = returned;
                        if (datatype == "html" || datatype == "text"){ $(display).hide().html(data).fadeIn(); }
                        if (datatype == "json"){ $(display).hide().autoRender(data).fadeIn(); }
                        $(loading).hide();
                    }
                },
                datatype
            );
            if ($event == 'submit') { return false;}
        }
    });
});
</script>

I want to reduce the amount of code used in this script, I think we can surely reduce the amount of code in this script by giving our attention to the line #11 which contains: if ( event == "keypress" ) {, because in the next else statement the same code is repeated twice, but how can we do this? Any idea?

The following piece looks duplicated:

                $.post(
                    $(select).attr("action"),
                    $(select).serialize(),
                    function(data){
                        if (datatype == "html" || datatype == "text"){ var returned = data; }
                        if (datatype == "json"){ var returned = data; }
                        if (returned != cache)
                        {
                            cache = returned;
                            if (datatype == "html" || datatype == "text"){ $(display).hide().html(data).fadeIn(); }
                            if (datatype == "json"){ $(display).hide().autoRender(data).fadeIn(); }
                            $(loading).hide();
                        }
                    },
                    datatype
                );

You should consider moving it's functionality to a function (sic)!

In addition to Vlad's answer: Remove the unnecessary if query and variable assignment:

$.post(
    $(select).attr("action"),
    $(select).serialize(),
    function(data) {

        // in every case, data is assigned to another variable which is
        // unnecessary as well
        // if (datatype == "html" || datatype == "text"){ var returned = data; }
        // if (datatype == "json"){ var returned = data; }

        if (data != cache) {
            cache = data;
        }

        if (datatype == "html" || datatype == "text") { 
            $(display).hide().html(data).fadeIn(); 
        }
        else if (datatype == "json"){ 
            $(display).hide().autoRender(data).fadeIn(); 
       }

       $(loading).hide();
   }
                }, datatype );