fix: generate tree-shakable bundles

Author: CreativeTechGuy

README.md

@@ -27,6 +27,8 @@
     -   [Mock HTML5 Canvas in JSDOM](#mock-html5-canvas-in-jsdom)
     -   [Mock an entire library](#mock-an-entire-library)
     -   [Mock complex objects](#mock-complex-objects)
+-   [Browser/Node Support](#browsernode-support)
+-   [Performance & Size](#performance--size)
 
 ## About
 
@@ -301,3 +303,11 @@ logoutHandler(req, res);
 // Assert that res.redirect() has been called
 expect(hasPathBeenVisited(res, ["redirect", ProxySymbol.APPLY])).toStrictEqual(true);
 ```
+
+## Browser/Node Support
+
+Out of the box we support all browsers that support the [Proxy object](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Proxy#browser_compatibility) and any current LTS version of Node. Unfortunately Proxy cannot be polyfilled for older versions so this is the best browser support we can do.
+
+## Performance & Size
+
+It's important to note that Proxies are far slower than most alternatives. We wouldn't recommend to use this for performance-critical code. The library is heavily tree-shakable so the average bundle size will be just a few KBs.

babel.config.js

@@ -1,20 +1,49 @@
-module.exports = {
-    presets: [
-        [
+const packageJSON = require("./package.json");
+
+const transformRuntimeVersion = packageJSON.devDependencies["@babel/plugin-transform-runtime"];
+
+module.exports = (api) => {
+    const isTest = api.env("test");
+    const config = {
+        plugins: [
+            [
+                "@babel/transform-runtime",
+                {
+                    corejs: 3,
+                    version: transformRuntimeVersion,
+                },
+            ],
+        ],
+        presets: [],
+    };
+    if (isTest) {
+        config.presets.push(
+            [
+                "@babel/env",
+                {
+                    bugfixes: true,
+                    useBuiltIns: "usage",
+                    corejs: 3,
+                    shippedProposals: true,
+                },
+            ],
+            [
+                "@babel/typescript",
+                {
+                    allowDeclareFields: true,
+                    onlyRemoveTypeImports: true,
+                },
+            ]
+        );
+    } else {
+        config.presets.push([
             "@babel/env",
             {
                 bugfixes: true,
-                useBuiltIns: "usage",
-                corejs: 3,
+                useBuiltIns: false,
                 shippedProposals: true,
             },
-        ],
-        [
-            "@babel/typescript",
-            {
-                allowDeclareFields: true,
-                onlyRemoveTypeImports: true,
-            },
-        ],
-    ],
+        ]);
+    }
+    return config;
 };