NativeScript · NathanWalker · Mar 16, 2026 · Mar 16, 2026 · Mar 16, 2026
diff --git a/packages/webpack5/__tests__/transformers/native-class.spec.ts b/packages/webpack5/__tests__/transformers/native-class.spec.ts
@@ -0,0 +1,211 @@
+import ts from 'typescript';
+import nativeClassTransformer from '../../src/transformers/NativeClass';
+
+function transform(input: string): string {
+	return ts.transpileModule(input, {
+		compilerOptions: {
+			module: ts.ModuleKind.ESNext,
+			target: ts.ScriptTarget.ES2022,
+			experimentalDecorators: true,
+			emitDecoratorMetadata: false,
+			useDefineForClassFields: false,
+		},
+		transformers: {
+			before: [nativeClassTransformer as ts.TransformerFactory<ts.SourceFile>],
+		},
+	}).outputText;
+}
+
+function countClassDeclarations(sourceText: string): number {
+	const sourceFile = ts.createSourceFile(
+		'/transformed.js',
+		sourceText,
+		ts.ScriptTarget.Latest,
+		true,
+		ts.ScriptKind.JS,
+	);
+
+	let count = 0;
+	const walk = (node: ts.Node) => {
+		if (ts.isClassDeclaration(node)) {
+			count++;
+		}
+		ts.forEachChild(node, walk);
+	};
+
+	walk(sourceFile);
+	return count;
+}
+
+describe('NativeClass transformer', () => {
+	describe('top-level classes', () => {
+		it('downlevels @NativeClass (no parentheses) to ES5 IIFE', () => {
+			const output = transform(`
+@NativeClass
+class Foo extends NSObject {}
+`);
+
+			expect(output).toContain('var Foo =');
+			expect(output).toContain('__extends(Foo, _super)');
+			expect(output).toContain('function (_super)');
+			expect(output).not.toContain('@NativeClass');
+			expect(countClassDeclarations(output)).toBe(0);
+		});
+
+		it('downlevels @NativeClass() (with parentheses) to ES5 IIFE', () => {
+			const output = transform(`
+@NativeClass()
+class Foo extends NSObject {}
+`);
+
+			expect(output).toContain('var Foo =');
+			expect(output).toContain('__extends(Foo, _super)');
+			expect(output).toContain('function (_super)');
+			expect(output).not.toContain('@NativeClass');
+			expect(countClassDeclarations(output)).toBe(0);
+		});
+
+		it('downlevels exported @NativeClass() class and preserves export', () => {
+			const output = transform(`
+@NativeClass()
+export class Bar extends NSObject {}
+`);
+
+			expect(output).toContain('var Bar =');
+			expect(output).toContain('__extends(Bar, _super)');
+			expect(output).toContain('export { Bar }');
+			expect(output).not.toContain('@NativeClass');
+			expect(countClassDeclarations(output)).toBe(0);
+		});
+
+		it('preserves prototype methods on the downleveled class', () => {
+			const output = transform(`
+@NativeClass()
+class Baz extends UIView {
+  doWork() { return 1; }
+}
+`);
+
+			expect(output).toContain('var Baz =');
+			expect(output).toContain('__extends(Baz, _super)');
+			expect(output).toContain('Baz.prototype.doWork = function ()');
+			expect(output).not.toContain('@NativeClass');
+		});
+
+		it('downlevels multiple @NativeClass() classes in the same file', () => {
+			const output = transform(`
+@NativeClass()
+class A extends NSObject {}
+@NativeClass()
+class B extends NSObject {}
+`);
+
+			expect(output).toContain('var A =');
+			expect(output).toContain('__extends(A, _super)');
+			expect(output).toContain('var B =');
+			expect(output).toContain('__extends(B, _super)');
+			expect(output).not.toContain('@NativeClass');
+			expect(countClassDeclarations(output)).toBe(0);
+		});
+
+		it('does NOT downlevel classes without @NativeClass', () => {
+			const output = transform(`
+class Plain extends Base {
+  method() {}
+}
+`);
+
+			expect(output).toContain('class Plain extends Base');
+			expect(output).not.toContain('var Plain =');
+			expect(output).not.toContain('__extends');
+			expect(countClassDeclarations(output)).toBe(1);
+		});
+
+		it('downlevels only the @NativeClass class when mixed with a plain class', () => {
+			const output = transform(`
+class Regular {}
+@NativeClass()
+class Native extends NSObject {}
+`);
+
+			expect(output).toContain('class Regular');
+			expect(output).toContain('var Native =');
+			expect(output).toContain('__extends(Native, _super)');
+			// Regular class stays as modern class declaration
+			expect(countClassDeclarations(output)).toBe(1);
+		});
+	});
+
+	describe('strip-loader marker', () => {
+		it('downlevels a class preceded by the /*__NativeClass__*/ marker', () => {
+			const output = transform(`
+/*__NativeClass__*/
+class Marked extends NSObject {}
+`);
+
+			expect(output).toContain('var Marked =');
+			expect(output).toContain('__extends(Marked, _super)');
+			expect(output).not.toContain('/*__NativeClass__*/');
+			expect(countClassDeclarations(output)).toBe(0);
+		});
+	});
+
+	describe('import cleanup', () => {
+		it('removes NativeClass from a named import while keeping other imports', () => {
+			const output = transform(`
+import { NativeClass, Observable } from '@nativescript/core';
+class Foo {}
+`);
+
+			expect(output).toContain("from '@nativescript/core'");
+			expect(output).toContain('Observable');
+			expect(output).not.toContain('NativeClass');
+		});
+
+		it('removes the entire import statement when NativeClass is the only import', () => {
+			const output = transform(`
+import { NativeClass } from '@nativescript/core';
+@NativeClass()
+class X extends NSObject {}
+`);
+
+			expect(output).not.toContain('NativeClass');
+			expect(output).toContain('var X =');
+			expect(output).toContain('__extends(X, _super)');
+		});
+	});
+
+	describe('nested scopes', () => {
+		it('downlevels @NativeClass() class declared inside a function body', () => {
+			const output = transform(`
+function test() {
+  @NativeClass()
+  class Test extends UIView {}
+}
+`);
+
+			expect(output).toContain('function test()');
+			expect(output).toContain('var Test =');
+			expect(output).toContain('__extends(Test, _super)');
+			expect(output).toContain('function (_super)');
+			expect(output).not.toContain('@NativeClass');
+			expect(countClassDeclarations(output)).toBe(0);
+		});
+
+		it('downlevels @NativeClass() class declared inside an arrow function body', () => {
+			const output = transform(`
+const test2 = () => {
+  @NativeClass()
+  class Test extends UIView {}
+};
+`);
+
+			expect(output).toContain('const test2 = () =>');
+			expect(output).toContain('var Test =');
+			expect(output).toContain('__extends(Test, _super)');
+			expect(output).toContain('function (_super)');
+			expect(output).not.toContain('@NativeClass');
+			expect(countClassDeclarations(output)).toBe(0);
+		});
+	});
+});
diff --git a/packages/webpack5/src/transformers/NativeClass/index.ts b/packages/webpack5/src/transformers/NativeClass/index.ts
@@ -279,8 +279,15 @@ export default function (context: ts.TransformationContext, ...args) {
 					result.push(updated);
 					continue;
 				}
-				// No deep traversal for unrelated nodes
-				result.push(statement);
+				// iterate over children as there might be a NativeClass inside of functions, blocks, etc
+				const visited = ts.visitEachChild(statement, visitNode, context);
+				if (visited !== statement) {
+					mutated = true;
+					changed = true;
+				}
+				if (visited) {
+					result.push(visited);
+				}
 			}
 			return [changed ? factory.createNodeArray(result) : statements, changed];
 		}