Copy + paste of the assets preloader from the soon-to-be released next version of UI Leaflet Integration plugin (https://github.com/ginsterbusch/ui-leaflet-integration ).

assets-loader-example.class.php

<?php
/**
 * @author Fabian Wolf (https://wp-devil.de)
 * @license GNU GPL v2 or later
 */
class AssetsPreloaderExample {
	function __construct() {
		add_action( 'wp', array( $this, 'preload_assets' ) );
		
		add_action( 'wp_enqueue_scripts', array( $this, 'init_assets' ) );
		
		
	}
	
	/**
	 * Test if current post contains one of "our" shortcodes and if so, load assets
	 *
	 * Struct:
	 * - Check in preload_assets if shortcodes are being used
	 * - if so, use add_action( 'wp_enqueue_scripts + init AND load_assets
	 * - done!
	 */
		
	function preload_assets() {
		$post_id = parent::get_post_id();
		
		//new __debug( $post_id, __METHOD__ );
		
		if( empty( $post_id ) ) {
			global $post;
			
			if( !empty( $post ) && isset( $post->ID) ) {
				$post_id = $post->ID;
			}
		}
		
		//new __debug( $post_id, __METHOD__ );
		
		if( !empty( $post_id ) ) {
			$current_post = get_post( $post_id );
			$arrTargets = array();
			
			//new __debug( $current_post, 'current_post - ' . __METHOD__ );
			//$current_post->post_content
			$post_meta = get_metadata( 'post', $post_id );
			
			//new __debug( $post_meta, 'post meta - ' . __METHOD__ );
			
			if( !empty( $post_meta ) ) {
				$arrTargets = $post_meta;
			}
			
			$arrTargets['post_content'] = $current_post->post_content;
			
			
			$arrMethods = $this->_get_methods_by( 'prefix', 'shortcode_' );
		
			//new __debug( $arrTargets, 'targets - ' . __METHOD__ );
			
			if( !empty( $arrMethods ) ) {
				foreach( $arrMethods as $strMethod ) { // avoid clashes with the sks helper shortcodes
					$strShortcode = str_replace( 'shortcode_', '', $strMethod );
					
					
					foreach( $arrTargets as $single_target ) { // cycle through possible DIFFERENT strings (what we search for is not necessarly contained in the regular post_content)
						
						if( is_array( $single_target ) ) {
							$strContentTarget = reset( $single_target );
						} else {
							$strContentTarget = $single_target;
						}
					
					
						if( strpos( $strContentTarget, '[' . $strShortcode ) !== false ) {
							$arrDetectedShortcode[ $strShortcode ] = 1;
						}
					}
			
				}
			}
				
		}
		
		//new __debug( $arrDetectedShortcode, 'detected shortcodes - ' . __METHOD__ );

		
		if( !empty( $arrDetectedShortcode ) ) { // load assets
		
			add_action( 'wp_enqueue_scripts', array( $this, 'init_assets' ) );
			add_action( 'wp_enqueue_scripts', array( $this, 'load_assets' ) );
		}
	}
}
?>