javascript - jQuery $.post problems (Not sending variable to PHP) -

i came across little problem , struggling solve it... wondering if had ideas... have read lot of stackoverflow posts same issues, still can't solve mine. workin in codeigniter.

i trying send variable php controller form view using jquery ($.post). here mine js code, embedded view:

$('#testbtn').on('click', function() {         var ordervalue = this.value;         $.post('http://localhost/codeigniter/welcome/index', {val: 'myvalue'}, function(data) {             alert(data);         });     }); 

here php code in controller:

$a = isset($_post['val']) ? $_post['val'] : 'not set yet.'; echo $a ; 

here button: <button id="testbtn" value="thevalue">button</button>

the button clicked, alert message variable , html code of whole page, php echo doesn't change, still says: "not set yet.".

basically seems easy, can't still find error...

without diving code more, work.

html:

<button id="testbtn" value="thevalue">button</button> 

javascript:

$('#testbtn').on('click', function() {         var ordervalue = {"ordervalue": $(this).val()};         $.ajax({         url: 'http://localhost/codeigniter/welcome/index',         method: 'post',         data: ordervalue,         success: function(data) { alert(data); }     }); 

php:

public function index() {     $a = isset($_post['ordervalue']) ? $_post['ordervalue'] : 'not set yet.';     return a; } 

as stated in other comments though, may not best practice.