adding a ajax hook not working in shortcode?

here is how it set up:
add_shortcode(‘abc_abc’,’shortfun’);

function shortfun()
{
include ‘ajax_res.php’;
}

—————————-in ajax_res.php:——————————————–
add_action(‘wp_ajax_ex_abc’,’ex_abc’);
function ex_abc()
{
echo ‘here!’;
die();
}

——————————-js call——————————-
jQuery.ajax({
type : “post”,
url : myAjax.ajaxurl,
data : {action: “ex_abc”},
success: function(response) {
alert(response);
}
}

why is the output always 0. and it looks like the function hooked onto the ajax call “ex_abc” is never called.
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