A Node.js upload handler that will write parts with a filename to disk to keep them out of memory, parts without a filename will not be parsed. Should be composed with another upload handler.


export const action = async ({
}: ActionFunctionArgs) => {
  const uploadHandler = unstable_composeUploadHandlers(
      maxPartSize: 5_000_000,
      file: ({ filename }) => filename,
    // parse everything else into memory
  const formData = await unstable_parseMultipartFormData(

  const file = formData.get("avatar");

  // file is a "NodeOnDiskFile" which implements the "File" API
  // ... etc


Property Type Default Description
avoidFileConflicts boolean true Avoid file conflicts by appending a timestamp on the end of the filename if it already exists on disk
directory string | Function os.tmpdir() The directory to write the upload.
file Function () => upload_${random}.${ext} The name of the file in the directory. Can be a relative path, the directory structure will be created if it does not exist.
maxPartSize number 3000000 The maximum upload size allowed (in bytes). If the size is exceeded a MaxPartSizeExceededError will be thrown.
filter Function OPTIONAL A function you can write to prevent a file upload from being saved based on filename, content type, or field name. Return false and the file will be ignored.

The function API for file and directory are the same. They accept an object and return a string. The object it accepts has filename, name, and contentType (all strings). The string returned is the path.

The filter function accepts an object and returns a boolean (or a promise that resolves to a boolean). The object it accepts has the filename, name, and contentType (all strings). The boolean returned is true if you want to handle that file stream.

Docs and examples licensed under MIT