What could go wrong..?

fun.js

import * as assert from 'assert';
import { MY_FLAG } from './trust';

assert.ok(MY_FLAG === 1);
setTimeout(function() {
  try {
    assert.ok(MY_FLAG === 1);
  } catch (err) {
    console.log('Just ES6 things.');
  }
}, 10);

trust.js

export let MY_FLAG = 1;
setTimeout(function() { MY_FLAG = 0; }, 0);

More realistic example:

// logger.js
export let logger = null;
export function initLogger(options) { logger = console; }
export function resetLogger() { logger = null; }

import { logger, initLogger } from './logger';
// Hey, let me bootstrap my framework!
if (config.log) { logger.init(config.log); }
// ...
if (logger) {
  // huh? how can this be null if I just checked it?
  page.on('changed', () => logger.info('New page load'));
}
// ...
// ... (and possibly in a different file)
// ...
import { resetLogger, logger } from './logger';
if (config.isProduction) { // TICKET-3411: Don't spam console in production
  resetLogger();
}
logger && logger.info('Yes, this change totally worked!');