admin-ajax call

gistfile1.php

<?php

function get_user_snippet(){
  $id = intval( $_GET['user_id'] );
  global $post;
  $post = get_post( $id );
  setup_postdata( $post );
  get_template_part( 'partials/user-snippet');
  exit;
}
add_action('wp_ajax_get_user_snippet', 'get_user_snippet');
add_action('wp_ajax_nopriv_get_user_snippet', 'get_user_snippet');

/* Build the URL with the following */ 
echo add_query_arg(
  array(
    'action' => 'get_user_snippet', 
    'user_id' => intval( 234 ),
  ),
  admin_url( 'admin-ajax.php' )
);