My js code:

$(function(){
    var arr = new Array('jj', 'kk', 'oo');
    $.post('test12.php', {'arr[]': arr}, function(data){
        alert(data);
    });
});

PHP code:

<?php
echo print_r($_POST['arr']);

The thing is,$.post receive a key named 'arr[]',it should be used in PHP as 'arr[]' instead of 'arr',but '$_POST['arr[]']' doesn't work,'arr' works.Which seems that Jquery might do something with curly braces '[]' before sending something to PHP.

Secondly,when I remove the single quotas around 'arr[]',PHP can not receive anything by using $_POST['arr'];,I don't know why?

Doing this task in a traditional way with no curly braces:

$.post('test12.php', {arr: arr}, function(data){
        alert(data);
    });

It works fine.

So when sending javascript array to PHP,why bothering using single quote and curly braces like

'arr[]'

instead of using a concise way like arr:arr

My return result is

Array(
   [0]=>jj
   [1]=>kk
   [2]=>oo
)
1

Notice there is a 1 under the array,why?