jquery - Post with AJAX and PHP - How is this really working -

1.) post content (i.e. text) id , variables in php in post.php file?

2.) call php, "if ($_post['promotion'])". how define _post in ajax , in php?

basically want php make post.

html:

<input type="text" id="promo_headline"> <button id="btnpostpromotion">post promotion</button> 

jquery:

$(document).ready(function(){ $('#btnpostpromotion').click(function() {     $.ajax({         type : 'post',         url : 'post.php',         datatype : 'json',         data: $('#promo_headline').val(),         success : function(data){                                if (data.error === true)             $('#errormodal').modal("show");         },         error : function(xmlhttprequest, textstatus, errorthrown) {             $('#errormodal').modal("show");         }     });      return false; }); }); 

php:

if ($_post['promotion']) {       $promo_headline = $_post['promo_headline']; } 

if want $_post['promotion'] available in php, send object key of promotion.

$.ajax({     url : '...',     type : 'post',     data : { promotion : $('#promo_headline').val() },     ... }); 

as note kinda makes me sad seeing jquery.val() being used when more efficient (and cross browser friendly) to:

document.getelementbyid('promo_headline').value;