file-upload.js

import axios from 'axios';
import { readFileSync } from 'fs';
const FormData = require('form-data');

const file = readFileSync('./whistle_v2.gcode', 'utf-8');

let form = new FormData();

form.append("file", file, {
  filepath: "whistle_v2.gcode"
});

form.getLength((err, length) => {  // This function is redundant
    const instance = axios.create({
        baseURL: 'http://localhost/api/',
        headers: {
            'X-Api-Key': '<api-key>',
        },
        timeout: 10000
    });

    instance.post('/files/local', form, {
    headers: {
        ...form.getHeaders(),
        'Content-Length': form.getLengthSync(),
    },
  }).then(res => {
            console.log(res.data);
        }).catch(err => {
            console.log(err);
    })
})