Add custom html or javascript in a popup by creating a shortcode

functions.php

<?php
/**
* Creates a shortcode [popups-code] that will print some html or js code
* We use buffer to capture raw html so you can paste it normally
**/
function popup_custom_code_func( $atts ) {
	$atts = shortcode_atts( array(
		'foo' => 'no foo',
	), $atts, 'bartag' );
 ob_start();?>
 
 <your html here>
 
 <?php
 $html = ob_get_contents();
 ob_clean();
 return $html;
}
add_shortcode( 'popups-code', 'popup_custom_code_func' );