Function createFormSubmitDestinationUrl

packages/next/src/client/form-shared.tsx:51–101

(
  action: string,
  formElement: HTMLFormElement
)

export type FormProps<RouteInferType = any> = InternalFormProps

export function createFormSubmitDestinationUrl(
  action: string,
  formElement: HTMLFormElement
) {
  let targetUrl: URL
  try {
    // NOTE: It might be more correct to resolve URLs relative to `document.baseURI`,
    // but we already do it relative to `location.href` elsewhere:
    //  (see e.g. https://github.com/vercel/next.js/blob/bb0e6722f87ceb2d43015f5b8a413d0072f2badf/packages/next/src/client/components/app-router.tsx#L146)
    // so it's better to stay consistent.
    const base = window.location.href
    targetUrl = new URL(action, base)
  } catch (err) {
    throw new Error(`Cannot parse form action "${action}" as a URL`, {
      cause: err,
    })
  }
  if (targetUrl.searchParams.size) {
    // url-encoded HTML forms *overwrite* any search params in the `action` url:
    //
    //  "Let `query` be the result of running the application/x-www-form-urlencoded serializer [...]"
    //  "Set parsed action's query component to `query`."
    //   https://html.spec.whatwg.org/multipage/form-control-infrastructure.html#submit-mutate-action
    //
    // We need to match that.
    // (note that all other parts of the URL, like `hash`, are preserved)
    targetUrl.search = ''
  }

  const formData = new FormData(formElement)

  for (let [name, value] of formData) {
    if (typeof value !== 'string') {
      // For file inputs, the native browser behavior is to use the filename as the value instead:
      //
      //   "If entry's value is a File object, then let value be entry's value's name. Otherwise, let value be entry's value."
      //   https://html.spec.whatwg.org/multipage/form-control-infrastructure.html#converting-an-entry-list-to-a-list-of-name-value-pairs
      //
      if (process.env.NODE_ENV === 'development') {
        console.warn(
          `<Form> only supports file inputs if \`action\` is a function. File inputs cannot be used if \`action\` is a string, ` +
            `because files cannot be encoded as search params.`
        )
      }
      value = value.name
    }

    targetUrl.searchParams.append(name, value)
  }
  return targetUrl
}

export function checkFormActionUrl(
  action: string,