add focus extension

packages/core/src/plugins/focus.ts

@@ -0,0 +1,28 @@
+import { Plugin } from 'prosemirror-state'
+import Editor from '../..'
+
+export default (editor: Editor) => new Plugin({
+  props: {
+    attributes: {
+      tabindex: '0',
+    },
+    handleDOMEvents: {
+      focus: () => {
+        editor.isFocused = true
+
+        const transaction = editor.state.tr.setMeta('focused', true)
+        editor.view.dispatch(transaction)
+
+        return true
+      },
+      blur: () => {
+        editor.isFocused = false
+
+        const transaction = editor.state.tr.setMeta('focused', false)
+        editor.view.dispatch(transaction)
+
+        return true
+      },
+    },
+  },
+})