document.querySelector('button[name="checkout"]') || document.querySelector('input[name="checkout"]'); b2bCheckbox.addEventListener("change", function () { gstFields.style.display = this.checked ? "block" : "none"; }); checkoutBtn.addEventListener("click", function (e) { if (b2bCheckbox.checked) { const gst = gstInput.value.trim(); const gstRegex = /^[0-9]{2}[A-Z]{5}[0-9]{4}[A-Z]{1}[1-9A-Z]{1}Z[0-9A-Z]{1}$/; if (!gstRegex.test(gst)) { e.preventDefault(); error.innerText = "Please enter a valid GSTIN."; error.style.display = "block"; gstInput.focus(); return false; } if (companyInput.value.trim() === "") { e.preventDefault(); error.innerText = "Company Name is required."; error.style.display = "block"; companyInput.focus(); return false; } } }); }); name="checkout" disabled form="cart" > Check out