Check the Google Tag Manager dataLayer for an Ecommerce transaction and do something only once (cookie enforced)

gistfile1.js

if (typeof (window.dataLayer) !== 'undefined' && window.dataLayer.length) {
    for (var d = 0; d < window.dataLayer.length; d++) {

        var obj = window.dataLayer[d],
            keys = Object.keys(obj);

        for (var k = 0; k < keys.length; k++) {
            var key = keys[k],
                val = obj[key];

            if (key == 'ecommerce') {
                var token = 'order-' + val.purchase.actionField.id;
                var sent = new RegExp(token).test(document.cookie);
                if (!sent) {
                    // Do Stuff
                    
                    // Set a cookie to not run again for an hour
                    var d = new Date(Date.now() + 3600000);
                    document.cookie = token + '=sent; expires=' + d.toGMTString() + '; path=' + window.location.pathname;
                }
            }
        }
    }
}