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