p5.js-web-editor/client/modules/IDE/actions/uploader.js

import axios from 'axios';
import { createFile } from './files';

const s3Bucket = `http://${process.env.S3_BUCKET}.s3.amazonaws.com/`;
const ROOT_URL = location.href.indexOf('localhost') > 0 ? 'http://localhost:8000/api' : '/api';

export function dropzoneAcceptCallback(file, done) {
  return () => {
    file.postData = []; // eslint-disable-line
    axios.post(`${ROOT_URL}/S3/sign`, {
      name: file.name,
      type: file.type,
      size: file.size,
      // _csrf: document.getElementById('__createPostToken').value
    },
      {
        withCredentials: true
      })
    .then(response => {
      file.custom_status = 'ready'; // eslint-disable-line
      file.postData = response.data; // eslint-disable-line
      file.s3 = response.data.key; // eslint-disable-line
      file.previewTemplate.className += ' uploading'; // eslint-disable-line
      done();
    })
    .catch(response => {
      file.custom_status = 'rejected'; // eslint-disable-line
      if (response.data.responseText && response.data.responseText.message) {
        done(response.data.responseText.message);
      }
      done('error preparing the upload');
    });
  };
}

export function dropzoneSendingCallback(file, xhr, formData) {
  return () => {
    Object.keys(file.postData).forEach(key => {
      formData.append(key, file.postData[key]);
    });
    formData.append('Content-type', '');
    formData.append('Content-length', '');
    formData.append('acl', 'public-read');
  };
}

export function dropzoneCompleteCallback(file) {
  return (dispatch, getState) => { // eslint-disable-line
    let inputHidden = '<input type="hidden" name="attachments[]" value="';
    const json = {
      url: `${s3Bucket}${file.postData.key}`,
      originalFilename: file.name
    };
    console.log(json, JSON.stringify(json), JSON.stringify(json).replace('"', '\\"'));
    inputHidden += `${window.btoa(JSON.stringify(json))}" />`;
    // document.getElementById('uploader').appendChild(inputHidden);
    document.getElementById('uploader').innerHTML += inputHidden;

    const formParams = {
      name: file.name,
      url: `${s3Bucket}${file.postData.key}`
    };
    createFile(formParams)(dispatch, getState);
  };
}