FormData everything converting to string even arrays

Question

const formData = new FormData()
formData.append('choices', [1, 2, 3])

choices converted to

'1,2,3'

And this is sent to node js which fails zod valdation because it is expecting array. this also same happens with numbers.

axios post request

axios.post('product', formData, {
      headers: {
        'Content-Type': 'multipart/form-data',
      },
    })

Answer 1

 const numArray = [1, 2, 3, 4, 5];
    const formData = new FormData();
    formData.append("data", JSON.stringify(numArray));

Post request

 await axios.post(url, formData, {
      headers: {
        "Content-Type": "multipart/form-data",
        Accept: "application/json",
      },
    });

Answer 2

The value for formData will be converted to a string.

See documentation: https://developer.mozilla.org/en-US/docs/Web/API/FormData/append

The field's value. This can be a USVString or Blob (including subclasses such as File). If none of these are specified the value is converted to a string.

You can convert it back on the server side with:

const choicesArray = choices.split(',').map(Number);