drupal ajax 分页,drupal call ajax function

$delete_commant = l(t('X'), $url, array('attributes' =>

array('onclick' => 'return call_ajax(123)')));

when i put alert in call_ajax function definition, it is alerted, so i proceed to write the ajax post method, but when i click the link page getting refresh,

How to implement ajax in drupal

function call_ajax(str){alert(str);

var url = "post.php";

var params = "lorem=ipsum&name=binny";

http.open("POST", url, true);

//Send the proper header information along with the request

http.setRequestHeader("Content-type", "application/x-www-form-urlencoded");

http.setRequestHeader("Content-length", params.length);

http.setRequestHeader("Connection", "close");

http.onreadystatechange = function() {//Call a function when the state changes.

if(http.readyState == 4 && http.status == 200) {

alert(http.responseText);

}

}

http.send(params);

}