Script Code
<script src="js/checkout.js" STRIPE_PUBLISHABLE_KEY="<?php echo STRIPE_PUBLISHABLE_KEY; ?>" defer></script>
with in the script
// Get API Key
let STRIPE_PUBLISHABLE_KEY = document.currentScript.getAttribute('STRIPE_PUBLISHABLE_KEY');
Script Code
<script src="js/checkout.js" STRIPE_PUBLISHABLE_KEY="<?php echo STRIPE_PUBLISHABLE_KEY; ?>" defer></script>
with in the script
// Get API Key
let STRIPE_PUBLISHABLE_KEY = document.currentScript.getAttribute('STRIPE_PUBLISHABLE_KEY');