Add babel class properties plugin

Author: artf

package.json

@@ -22,6 +22,7 @@
   "license": "BSD-3-Clause",
   "dependencies": {
     "@babel/core": "^7.13.10",
+    "@babel/plugin-proposal-class-properties": "^7.13.0",
     "@babel/plugin-transform-runtime": "^7.13.10",
     "@babel/preset-env": "^7.13.12",
     "@babel/runtime": "^7.13.10",

src/utils.js

@@ -86,5 +86,8 @@ export const babelConfig = (opts = {}) => ({
             // corejs: 3,
         } ]
     ],
-    plugins: [ '@babel/plugin-transform-runtime' ],
+    plugins: [
+        '@babel/plugin-transform-runtime',
+        ['@babel/plugin-proposal-class-properties', { loose: true }],
+    ],
 })