How to send File uploads using fetch via Netlify forms?

I can’t find any documentation on file uploads for Netlify forms using fetch for submission.

I am using Formik with yup for validation and need to send a form with a range of fields, including one field with multiple file uploads.

The form is successfully posting to Netlify with all other data using Object.keys, encodeURIComponent and .join("&"). But this won’t work for Files as it needs to send the File object. Any idea how I can send this data along with other fields so that Netlify recognises and has access to the files from the Form alongside this data?

This article was useful to get me so far with encoding data to post via fetch, but not for files.

Really appreciate the help.

Hi @danwebb, while there is no documentation that specifically covers file uploads for react apps, we do have an example in a repo from the author of that article. Let me know if that helps.

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Thank you for the reply Dennis. Looks like that could be useful yes.
I’ll let you know how I get on.

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Using that repo as a guide, I was able to get a ‘single’ File sent after validation. However I can’t seem to get Netlify to recognise multiple files within the Filelist object that is sent for a single field. I even tried creating a new array with the given File objects instead, but the response for that field Netlify side is then blank:

function encode(data) {
const formData = new FormData();

for (const key of Object.keys(data)) {
    if(key === 'repairs_files'){
        const files = Object.entries(data[key]);
        let filesArr = []; => {
           return filesArr.push(file[1]);
        formData.append(key, filesArr);
    } else {
        formData.append(key, data[key]);
return formData;


So I guess the question is in what format does Netlify accept ‘multiple’ File uploads for a single field. Or does it only accept single File uploads? And therefore I’d need to create 3 fields for single File uploads?

Yup, I think we have an unstated limit of one file upload per field. Does that work better for you if you reconfigure it to be one-per?

Sure, thanks for letting me know. Yeah, I’ll need to modify the UI and will let the client know it’s not currently achievable in one field.

It might be useful to add that to the Forms docs, as I spent quite a while establishing whether it would work or not. Keep up the good work :slight_smile:

Great suggestion, Dan. We got an enhancement request filed with our documentarians :slight_smile: