ajax in wordpress return content-none file

In my funcitons.php file i have function that response to ajax call and return posts:
functions.php:

function returnPosts(){
    if ( have_posts() ) {
    		while ( have_posts() ) {
    			the_post();
    			get_template_part('content', get_post_format());
    		}
    	} else {
    		get_template_part( 'content', 'none' );
    	}
    exit();
    }

    add_action('wp_ajax_returnPosts', 'returnPosts');
    add_action('wp_ajax_nopriv_returnPosts', 'returnPosts');

Javascript (in index.php):

jQuery.ajax({
        type:"POST",
        url: "<?php echo admin_url("admin-ajax.php"); ?>",
        data: {"action": "returnPosts"},
        success:function(results){
            // Work with results
        }
    });

But when i call this function via JS i always get content from content-none.php file.