[client-app] Convert nylas-env.coffee to ES6 😓

Test Plan: unit tests + run the app

Reviewers: juan, halla, evan

Reviewed By: evan

Differential Revision: https://phab.nylas.com/D3979

packages/client-app/src/window-bootstrap.coffee

@@ -1,19 +0,0 @@
-# Swap out Node's native Promise for Bluebird, which allows us to
-# do fancy things like handle exceptions inside promise blocks
-global.Promise = require 'bluebird'
-Promise.setScheduler(global.setImmediate)
-
-# Like sands through the hourglass, so are the days of our lives.
-require './window'
-
-NylasEnvConstructor = require './nylas-env'
-window.NylasEnv = window.atom = NylasEnvConstructor.loadOrCreate()
-NylasEnv.initialize()
-NylasEnv.startRootWindow()
-
-
-# Workaround for focus getting cleared upon window creation
-windowFocused = ->
-  window.removeEventListener('focus', windowFocused)
-  setTimeout (-> document.getElementById('sheet-container')?.focus()), 0
-window.addEventListener('focus', windowFocused)

packages/client-app/src/window-bootstrap.es6

@@ -0,0 +1,25 @@
+/* eslint import/first: 0 */
+
+// Swap out Node's native Promise for Bluebird, which allows us to
+// do fancy things like handle exceptions inside promise blocks
+global.Promise = require('bluebird');
+Promise.setScheduler(global.setImmediate);
+
+// Like sands through the hourglass, so are the days of our lives.
+import './window';
+
+import NylasEnvConstructor from './nylas-env';
+window.NylasEnv = NylasEnvConstructor.loadOrCreate();
+NylasEnv.initialize();
+NylasEnv.startRootWindow();
+
+
+// Workaround for focus getting cleared upon window creation
+const windowFocused = () => {
+  window.removeEventListener('focus', windowFocused);
+  return setTimeout((() => {
+    const elt = document.getElementById('sheet-container');
+    if (elt) elt.focus();
+  }), 0);
+}
+window.addEventListener('focus', windowFocused);