I am trying to add a product to the cart with shopify fetch api. I have created this code, but I can not add the product to the cart. any help please?

let submitButton = document.getElementById('submit');
let variantId = submitButton.getAttribute('data-variant-id');

let newVariantIdArray = variantId.split(',');

let product_data = newVariantIdArray.map(variantId => {
    return {quantity: 1, id: variantId}
  })

let data = {
    items: product_data
  }
   

function addToCart(data) {
  const cartData = data

  fetch('/cart/add.js', {
    method: 'POST',
    headers: { 'Content-Type': 'application/json' },
    body: JSON.stringify(cartData),
  })
    .then((response) => {
      if (response.ok) {
      }
    })
    .catch((error) => console.error(error))
}

submitButton.addEventListener('click', (event) => {
  event.preventDefault()

  addToCart(variantId)
})

console.log(data)