function maybePrefixUrlField() {
if (this.value.trim() !== '' && this.value.indexOf('http') !== 0) {
this.value = "http://" + this.value;
}
}
var urlFields = document.querySelectorAll('.mc4wp-form input[type="url"]');
if (urlFields) {
for (var j=0; j < urlFields.length; j++) {
urlFields[j].addEventListener('blur', maybePrefixUrlField);
}
}