paypal-checkout-loader.js

<script>
    (function() {
        var PAYPAL_SCRIPT = 'https://www.paypalobjects.com/api/checkout.js';
        var ATTEMPTS = 3;
    
        function loadPayPalCheckout(callback) {
            
            ATTEMPTS -= 1;
            
            var container = document.body || document.head;
            callback = callback || function() {};

            var script = document.createElement('script');
            script.setAttribute('src', PAYPAL_SCRIPT);

            script.onload = function() {
                callback()
            };
            
            script.onerror = function(err) {
                if (ATTEMPTS) {
                    loadPayPalCheckout(callback);
                } else {
                    callback(err)
                }
            };
            
            container.appendChild(script);
        }

        loadPayPalCheckout(function(err) {
            if (err) {
                // fallback to static button
            } else {
                // paypal.Button is ready
            }
        });
    })();
</script>