$(document).ready( function() {
    // Code here
});

$.post( url, sendData, callback(data) {
});

var sendData = {
    id : 2,
    action : 'delete'
};
	

var sendData = {
    val : $('#calc').val()
};
$.post('/double.php', sendData,
 function(data) {
    $('#calc').val(data);
});
	

$('#loading').show();
$.post('/double.php', sendData, function(data) {
    $('#calc').val(data);
    $('#loading').hide();
});
	

<div data-id="5">
<article data-author="Bilbo Baggins">
<section data-is-awesome="true">

$('article').data('author');
$('article').data('author', 'Frodo Baggins');

<div data-id="5">
    <h2>Canon 70D</h2>
    <a>Add to cart</a>
    <span class="counter"></span>
</div>
<div data-id="6">
    <h2>Nikon D5300</h2>
    <a>Add to cart</a>
    <span class="counter"></span>
</div>
	

$('#cart a').click( function(e) {
    e.preventDefault();
    var $el = $(this).closest('div');

    var sendData = {
        id: $el.data('id')
    };
    ...

    $.post('/add.php', sendData,
   function(data) {
        if( data.success ) {
            $el.find('.counter')
    .html(data.total);
        }
    }, 'json');
});