Hypothetical effects API for microstates

uploader-controller.js

import { act, every } from '@microstates/effects';

/**
 * An effects function matches the state emitted by the store using
 * the specified patterns. For every time the pattern is recognized, 
 * execute the callback with the matching object.
 *
 * This particular effects function recognizes every upload that is 
 * brand new and initiates the XHR, and also every upload that has
 * been cancelled by the user and aborts it.
 */
export default act
  .on({ uploads: every({ isNew: true })}, upload => {
    let xhr = new XMLHttpRequest();
    xhr.open('POST', URL);
    xhr.onload = () => current = current.finish(xhr)
    xhr.upload.onprogress = e => current = current.progress(e);
    xhr.send(upload.file);
    let current = upload.start(xhr);
  })
  .on({ uploads: every({ isCancelled: true })}, upload => {
    let { xhr } = upload.state;
    delete xhr.onload;
    delete xhr.upload.onprogress;
    xhr.abort();
    upload.abort();
  })