Alert the Attachment id of the media that is being upload

functions.php

<?php
if ( ! function_exists( 'wp_footer_rtmedia_add_script_callback' ) ) {
	/**
	 * Add javascript in the footer
	 */
	function wp_footer_rtmedia_add_script_callback() {
		?>
		<script type="text/javascript">
			jQuery(document).ready(function($) {
				rtMediaHook.register('rtmedia_js_after_file_upload', function ( resp ) {
					if ( jQuery.type( resp ) == 'array' ) {
						if ( typeof resp[2] != 'undefined' ) {
							media_obj = JSON.parse( resp[ 2 ] );
							// Check for attachment_id exists or not.
							if ( typeof media_obj !== 'undefined' && typeof media_obj.attachment_id !== 'undefined' ) {
								// Check for media_type exists or not and it media_type should be 'photo' only.
								if ( typeof media_obj.media_type !== 'undefined' && media_obj.media_type == 'photo' ) {
									// Alert Media id
									alert( media_obj.attachment_id );
								}
							}
						}
					}
					return true;
				});
			});
		</script>
		<?php
	}
}
add_action( 'wp_footer', 'wp_footer_rtmedia_add_script_callback', 10 );






if ( ! function_exists( 'rtmedia_upload_endpoint_response_callback' ) ) {
	/**
	 * Add more varibale after the media is being uploaded

	 * @param array $data

	 * @return array
	 */
	function rtmedia_upload_endpoint_response_callback( $data = array() ){
		if ( class_exists( 'RTMediaMedia' ) && is_array( $data ) && isset( $data['media_id'] ) && ! empty( $data['media_id'] ) ) {
			$media_id = intval( $data['media_id'] );
			$media_obj    = new RTMediaMedia();
			$media        = $media_obj->model->get( array( 'id' => $media_id ) );
			if ( isset( $media ) && count( $media ) > 0 ) {
				$data['attachment_id'] = $media[0]->media_id;
				$data['media_type'] = $media[0]->media_type;
			}
		}
		return $data;
	}
}
add_filter( 'rtmedia_upload_endpoint_response', 'rtmedia_upload_endpoint_response_callback', 10, 1 );

It alert attachment id that has been added from the rtMedia upload section.
It also checks for the media_type equal to 'photo' only. We can change media type as per our need.