fix: make ReactiveFlags able to treeshake in esm

Author: johnsoncodehk

build.js

@@ -54,5 +54,13 @@ cjsProgram.emit(undefined, (fileName, text) => {
 esmProgram.emit(undefined, (fileName, text) => {
 	fileName = fileName.slice(0, -'.js'.length) + '.mjs';
 	text = text.replace(/\.\/system\.js/g, './system.mjs');
+	text = text.replace(
+		`var ReactiveFlags;\n(function (ReactiveFlags)`,
+		`var ReactiveFlags = /*#__PURE__*/(function (ReactiveFlags = {})`,
+	);
+	text = text.replace(
+		`})(ReactiveFlags || (ReactiveFlags = {}));`,
+		`    return ReactiveFlags;\n})();`,
+	)
 	ts.sys.writeFile(fileName, text);
 });

size.js

@@ -3,18 +3,22 @@ require('./build.js');
 const rolldown = require('rolldown');
 
 rolldown.build({
-	input: 'esm/index.mjs', output: { minify: true }, write: false
+	input: 'esm/index.mjs', output: { minify: true }, write: false, treeshake: true
 }).then(built => {
 	console.log(`esm/index.mjs: ${(built.output[0].code.length / 1024).toFixed(2)} KB`);
 });
 rolldown.build({
-	input: 'esm/system.mjs', output: { minify: true }, write: false
+	input: 'esm/system.mjs', output: { minify: true }, write: false, treeshake: true
 }).then(built => {
 	console.log(`esm/system.mjs: ${(built.output[0].code.length / 1024).toFixed(2)} KB`);
 });
-rolldown.build({ input: 'cjs/index.cjs', output: { minify: true }, write: false }).then(built => {
+rolldown.build({
+	input: 'cjs/index.cjs', output: { minify: true }, write: false, treeshake: true
+}).then(built => {
 	console.log(`cjs/index.cjs: ${(built.output[0].code.length / 1024).toFixed(2)} KB`);
 });
-rolldown.build({ input: 'cjs/system.cjs', output: { minify: true }, write: false }).then(built => {
+rolldown.build({
+	input: 'cjs/system.cjs', output: { minify: true }, write: false, treeshake: true
+}).then(built => {
 	console.log(`cjs/system.cjs: ${(built.output[0].code.length / 1024).toFixed(2)} KB`);
 });