proposal: trojan horse private methods

Author: rax-it

packages/@lwc/babel-plugin-component/src/constants.ts

@@ -34,6 +34,7 @@ const TEMPLATE_KEY = 'tmpl';
 const COMPONENT_NAME_KEY = 'sel';
 const API_VERSION_KEY = 'apiVersion';
 const COMPONENT_CLASS_ID = '__lwc_component_class_internal';
+const PRIVATE_METHOD_PREFIX = '__lwc_component_class_internal_private_';
 
 export {
     DECORATOR_TYPES,
@@ -46,4 +47,5 @@ export {
     COMPONENT_NAME_KEY,
     API_VERSION_KEY,
     COMPONENT_CLASS_ID,
+    PRIVATE_METHOD_PREFIX,
 };

packages/@lwc/babel-plugin-component/src/index.ts

@@ -15,6 +15,8 @@ import dedupeImports from './dedupe-imports';
 import dynamicImports from './dynamic-imports';
 import scopeCssImports from './scope-css-imports';
 import compilerVersionNumber from './compiler-version-number';
+import privateMethodTransform from './private-method-transform';
+import reversePrivateMethodTransform from './reverse-private-method-transform';
 import { getEngineImportSpecifiers } from './utils';
 import type { BabelAPI, LwcBabelPluginPass } from './types';
 import type { PluginObj } from '@babel/core';
@@ -33,13 +35,16 @@ export default function LwcClassTransform(api: BabelAPI): PluginObj<LwcBabelPlug
     const { Class: transformDecorators } = decorators(api);
     const { Import: transformDynamicImports } = dynamicImports();
     const { ClassBody: addCompilerVersionNumber } = compilerVersionNumber(api);
+    const { Program: transformPrivateMethods } = privateMethodTransform(api);
+    const { ClassMethod: reverseTransformPrivateMethods } = reversePrivateMethodTransform(api);
 
     return {
         manipulateOptions(opts, parserOpts) {
             parserOpts.plugins.push('classProperties', [
                 'decorators',
                 { decoratorsBeforeExport: true },
             ]);
+            parserOpts.plugins.push('privateMethods');
         },
 
         visitor: {
@@ -54,6 +59,15 @@ export default function LwcClassTransform(api: BabelAPI): PluginObj<LwcBabelPlug
 
                     // Add ?scoped=true to *.scoped.css imports
                     scopeCssImports(api, path);
+
+                    // Transform private methods BEFORE any other plugin processes them
+                    if (
+                        transformPrivateMethods &&
+                        typeof transformPrivateMethods === 'object' &&
+                        'enter' in transformPrivateMethods
+                    ) {
+                        (transformPrivateMethods as any).enter(path, state);
+                    }
                 },
                 exit(path) {
                     const engineImportSpecifiers = getEngineImportSpecifiers(path);
@@ -68,6 +82,8 @@ export default function LwcClassTransform(api: BabelAPI): PluginObj<LwcBabelPlug
 
             Class: transformDecorators,
 
+            ClassMethod: reverseTransformPrivateMethods,
+
             ClassBody: addCompilerVersionNumber,
 
             ExportDefaultDeclaration: transformCreateRegisterComponent,

playground/src/modules/x/counter/counter.js

@@ -10,5 +10,8 @@ export default class extends LightningElement {
     }
     decrement() {
         this.counter--;
+        this.#something();
     }
+
+    #something() {}
 }