Set loose in the global map

packages/babel-plugin-proposal-enhanced-classes/src/features.js

@@ -15,6 +15,7 @@ export const FEATURES = Object.freeze({
 //      - node_modules
 //        - @babel-plugin-proposal-enhanced-classes
 const featuresKey = "@babel/plugin-proposal-enhanced-classes/featuresKey";
+const looseKey = "@babel/plugin-proposal-enhanced-classes/looseKey";
 
 export function enableFeature(file, feature) {
   file.set(featuresKey, file.get(featuresKey) | feature);
@@ -59,3 +60,16 @@ export function verifyUsedFeatures(path, file) {
     }
   }
 }
+
+// Set "loose". The original value isn't overwritten, so
+//   @babel/plugin-class-properties { loose: true }
+//   @babel/plugin-class-properties { loose: false }
+// is transformed in loose mode.
+export function setLoose(file, loose) {
+  const oldLoose = file.get(looseKey);
+  if (oldLoose === undefined) file.set(looseKey, loose);
+}
+
+export function isLoose(file) {
+  return !!file.get(looseKey);
+}

packages/babel-plugin-proposal-enhanced-classes/src/index.js

@@ -8,7 +8,13 @@ import {
   buildFieldsInitNodes,
 } from "./fields";
 import { injectInitialization, extractComputedKeys } from "./misc";
-import { enableFeature, verifyUsedFeatures, FEATURES } from "./features";
+import {
+  enableFeature,
+  verifyUsedFeatures,
+  FEATURES,
+  setLoose,
+  isLoose,
+} from "./features";
 
 export default declare((api, options) => {
   api.assertVersion(7);
@@ -24,6 +30,8 @@ export default declare((api, options) => {
     },
 
     pre() {
+      setLoose(this.file, loose);
+
       if (instanceFields) enableFeature(this.file, FEATURES.instanceFields);
       if (staticFields) enableFeature(this.file, FEATURES.staticFields);
       if (privateMethods) enableFeature(this.file, FEATURES.privateMethods);
@@ -33,6 +41,7 @@ export default declare((api, options) => {
     visitor: {
       Class(path, state) {
         verifyUsedFeatures(path, this.file);
+        const loose = isLoose(this.file);
 
         let constructor;
         const props = [];

packages/babel-plugin-proposal-enhanced-classes/test/fixtures/plugin-proposal-class-properties/loose-not-overwritten/input.js

@@ -0,0 +1,3 @@
+class A {
+  foo;
+}

packages/babel-plugin-proposal-enhanced-classes/test/fixtures/plugin-proposal-class-properties/loose-not-overwritten/options.json

@@ -0,0 +1,6 @@
+{
+  "plugins": [
+    ["proposal-class-properties", { "loose": true }, "name 1"],
+    ["proposal-class-properties", { "loose": false }, "name 2"]
+  ]
+}

packages/babel-plugin-proposal-enhanced-classes/test/fixtures/plugin-proposal-class-properties/loose-not-overwritten/output.js

@@ -0,0 +1,6 @@
+class A {
+  constructor() {
+    this.foo = void 0;
+  }
+
+}

packages/babel-plugin-proposal-enhanced-classes/test/index.js

@@ -0,0 +1,3 @@
+import runner from "@babel/helper-plugin-test-runner";
+
+runner(__dirname);