[javascript] How to post a file from a form with Axios

Using raw HTML when I post a file to a flask server using the following I can access files from the flask request global:

<form id="uploadForm" action='upload_file' role="form" method="post" enctype=multipart/form-data>
    <input type="file" id="file" name="file">
    <input type=submit value=Upload>
</form>

In flask:

def post(self):
    if 'file' in request.files:
        ....

When I try to do the same with Axios the flask request global is empty:

<form id="uploadForm" enctype="multipart/form-data" v-on:change="uploadFile">
<input type="file" id="file" name="file">
</form>

uploadFile: function (event) {
    const file = event.target.files[0]
    axios.post('upload_file', file, {
        headers: {
          'Content-Type': 'multipart/form-data'
        }
    })
}

If I use the same uploadFile function above but remove the headers json from the axios.post method I get in the form key of my flask request object a csv list of string values (file is a .csv).

How can I get a file object sent via axios?

How to post file using an object in memory (like a JSON object):

import axios from 'axios';
import * as FormData  from 'form-data'

async function sendData(jsonData){
    // const payload = JSON.stringify({ hello: 'world'});
    const payload = JSON.stringify(jsonData);
    const bufferObject = Buffer.from(payload, 'utf-8');
    const file = new FormData();

    file.append('upload_file', bufferObject, "b.json");

    const response = await axios.post(
        lovelyURL,
        file,
        headers: file.getHeaders()
    ).toPromise();


    console.log(response?.data);
}

This works for me, I hope helps to someone.

var frm = $('#frm');
let formData = new FormData(frm[0]);
axios.post('your-url', formData)
    .then(res => {
        console.log({res});
    }).catch(err => {
        console.error({err});
    });

If you don't want to use a FormData object (e.g. your API takes specific content-type signatures and multipart/formdata isn't one of them) then you can do this instead:

uploadFile: function (event) {
    const file = event.target.files[0]
    axios.post('upload_file', file, {
        headers: {
          'Content-Type': file.type
        }
    })
}

Sample application using Vue. Requires a backend server running on localhost to process the request:

var app = new Vue({
  el: "#app",
  data: {
    file: ''
  },
  methods: {
    submitFile() {
      let formData = new FormData();
      formData.append('file', this.file);
      console.log('>> formData >> ', formData);

      // You should have a server side REST API 
      axios.post('http://localhost:8080/restapi/fileupload',
          formData, {
            headers: {
              'Content-Type': 'multipart/form-data'
            }
          }
        ).then(function () {
          console.log('SUCCESS!!');
        })
        .catch(function () {
          console.log('FAILURE!!');
        });
    },
    handleFileUpload() {
      this.file = this.$refs.file.files[0];
      console.log('>>>> 1st element in files array >>>> ', this.file);
    }
  }
});

https://codepen.io/pmarimuthu/pen/MqqaOE