Data transfer from JavaScript to PHP

You would have to make an AJAX call from JavaScript to a PHP script. That PHP script would save the screen resolution in the current session (you'll need to use sessions for this). A PHP script requested at a later point could then access the screen resolution as passed by the JavaScript snippet.

First, you need to change $.toJSON(asetid) to JSON.stringify(asetid). But, if, somehow you still want to use $.toJSON(asetid), you need to include the jquery-json plugin from http://code.google.com/p/jquery-json/ on your page.

Second, I think the ajax request part should be put outside of the iterator function, otherwise, you will be making an ajax request for each row of the table. Here is the revised code:

var Dataconvert;
var asetid = new Array();
$("#simpanmodifikasi").click(function(){
    var table = $('#tableasal tbody');
    table.find('tr').each(function (row, input) {
        // var coba = $(this).find('input'),
        // asetid = coba.eq(0).val();
        asetid[row] = {
            "asetid" : $(this).find('input:eq(0)').val(),
            "namabarang" : $(this).find('input:eq(1)').val(),
        }
    });
  
    //these should be outside the 'each' iterator
    Dataconvert = JSON.stringify(asetid);
    $.ajax({
        url:"<?php echo site_url('fixed/modification/tes');?>",
        type:"POST",
        data:Dataconvert,
        dataType : 'json',
        cache : false,
        success:function(html){
           alert(html);
         }
    })
})

Third, now the answer to your question. The ajax request will send the stringified JSON in the POST body. Example:

[{"asetid":"10","namabarang":"Buku"},{"asetid":"30","namabarang":"Laptop"}]

To read it from the PHP side (the fixed/modification/tes script), you can manually read it from the standard input and parse it using json_decode.

<?php
$data = json_decode(file_get_contents('php://input'), true);
print_r($data);
?>

which will result in something like this:

Array
(
    [0] => Array
        (
            [asetid] => 10
            [namabarang] => Buku
        )

    [1] => Array
        (
            [asetid] => 30
            [namabarang] => Laptop
        )

)

AJAX is suitable for sending large amounts of code. Take a look at jQuery.post and jQuery.ajax. Special characters pass through POST-request unchanged.

Make sure you set php setting magic_quotes_gpc to off, as this option tells PHP to escape any special character with backslash.