Unable to use createReadStream with Node 18 FormData

Question

Previously to Node 18 releasing fetch/FormData we could do:

import FormData from 'form-data'

const form = new FormData();
form.append('my_field', 'my value');
form.append('my_buffer', new Buffer(10));
form.append('my_file', fs.createReadStream('/foo/bar.jpg'));

However with the global FormData I can no longer pass a stream - the error at the "my_file" line is:

Argument of type 'ReadStream' is not assignable to parameter of type 'string | Blob'

I know this is still experimental so potentially a bug or is there an alternative way to do this - besides reading the entire file as a string...

Answer 1

Node v18's native FormData is an implementation of the w3 FormData interface so you need to use that API.

The append() method accepts a Blob so you should be able to use the blob stream consumer

import { createReadStream } from 'node:fs';
import { blob } from 'node:stream/consumers';

// assuming a valid async context for brevity
const file = await blob(createReadStream("/foo/bar.jpg"));

const formData = new FormData();
formData.append("my_file", file, "bar.jpg");