standalone_button.html

<!-- Detect checkout.js eligibility -->

<script>
    if (paypal.isEligible()) {
       paypal.Button.render({ ... }, '#container'); 
    }
</script>


<!-- Otherwise render static button with redirect -->

<script src="https://www.paypalobjects.com/api/button.js"></script>

<div id="paypal-static-button"></div>

<script>
    var el = window.paypal.button.create('walmart', {
        lc: 'en_US',
        color: 'gold',
        shape: 'rect',
        size: 'small'
    }, {
        type: "button",
        label: 'checkout'
    }).el;

    document.querySelector('#paypal-static-button').appendChild(el);

    el.addEventListener('click', function(event) {
        event.preventDefault();

        // Generate EC token and redirect to paypal
    });
</script>