add: forum/components/CommentPostPreview

- This has been extracted from CommentPost

js/src/forum/components/CommentPostPreview.js

@@ -0,0 +1,33 @@
+/*global s9e*/
+
+import Component from "../../common/Component";
+
+export default class CommentPostPreview extends Component {
+  view() {
+    return <div className="Post-preview" />;
+  }
+
+  oncreate(vnode) {
+    super.oncreate(vnode);
+
+    // Every 50ms, if the composer content has changed, then update the post's
+    // body with a preview.
+    let preview;
+    const updatePreview = () => {
+      const content = app.composer.fields.content();
+
+      if (preview === content) return;
+
+      preview = content;
+
+      s9e.TextFormatter.preview(preview || '', vnode.dom);
+    };
+    updatePreview();
+
+    this.updateInterval = setInterval(updatePreview, 50);
+  }
+
+  onremove(vnode) {
+    clearInterval(this.updateInterval);
+  }
+}