Finalized theme loading and stuff

app/javascript/packs/share.js

@@ -0,0 +1,22 @@
+import loadPolyfills from '../mastodon/load_polyfills';
+
+function loaded() {
+  const ComposeContainer = require('../mastodon/containers/compose_container').default;
+  const React = require('react');
+  const ReactDOM = require('react-dom');
+  const mountNode = document.getElementById('mastodon-compose');
+
+  if (mountNode !== null) {
+    const props = JSON.parse(mountNode.getAttribute('data-props'));
+    ReactDOM.render(<ComposeContainer {...props} />, mountNode);
+  }
+}
+
+function main() {
+  const ready = require('../mastodon/ready').default;
+  ready(loaded);
+}
+
+loadPolyfills().then(main).catch(error => {
+  console.error(error);
+});