Implement using Proxy

.travis.yml

@@ -3,4 +3,3 @@ node_js:
   - '12'
   - '10'
   - '8'
-  - '6'

index.js

@@ -1,6 +1,6 @@
 'use strict';
 
-const processFn = (fn, options) => function (...args) {
+const processFn = (fn, options, proxy, unwrapped) => function (...args) {
 	const P = options.promiseModule;
 
 	return new P((resolve, reject) => {
@@ -29,10 +29,13 @@ const processFn = (fn, options) => function (...args) {
 			args.push(resolve);
 		}
 
-		fn.apply(this, args);
+		const self = this === proxy ? unwrapped : this;
+		Reflect.apply(fn, self, args);
 	});
 };
 
+const filterCache = new WeakMap();
+
 module.exports = (input, options) => {
 	options = Object.assign({
 		exclude: [/.+(Sync|Stream)$/],
@@ -45,24 +48,65 @@ module.exports = (input, options) => {
 		throw new TypeError(`Expected \`input\` to be a \`Function\` or \`Object\`, got \`${input === null ? 'null' : objType}\``);
 	}
 
-	const filter = key => {
-		const match = pattern => typeof pattern === 'string' ? key === pattern : pattern.test(key);
-		return options.include ? options.include.some(match) : !options.exclude.some(match);
+	const filter = (target, key) => {
+		let cached = filterCache.get(target);
+
+		if (!cached) {
+			cached = {};
+			filterCache.set(target, cached);
+		}
+
+		if (key in cached) {
+			return cached[key];
+		}
+
+		const match = pattern => (typeof pattern === 'string' || typeof key === 'symbol') ? key === pattern : pattern.test(key);
+		const desc = Reflect.getOwnPropertyDescriptor(target, key);
+		const writableOrConfigurableOwn = (desc === undefined || desc.writable || desc.configurable);
+		const included = options.include ? options.include.some(match) : !options.exclude.some(match);
+		const shouldFilter = included && writableOrConfigurableOwn;
+		cached[key] = shouldFilter;
+		return shouldFilter;
 	};
 
-	let ret;
-	if (objType === 'function') {
-		ret = function (...args) {
-			return options.excludeMain ? input(...args) : processFn(input, options).apply(this, args);
-		};
-	} else {
-		ret = Object.create(Object.getPrototypeOf(input));
-	}
+	const cache = new WeakMap();
 
-	for (const key in input) { // eslint-disable-line guard-for-in
-		const property = input[key];
-		ret[key] = typeof property === 'function' && filter(key) ? processFn(property, options) : property;
-	}
+	const proxy = new Proxy(input, {
+		apply(target, thisArg, args) {
+			const cached = cache.get(target);
+
+			if (cached) {
+				return Reflect.apply(cached, thisArg, args);
+			}
+
+			const pified = options.excludeMain ? target : processFn(target, options, proxy, target);
+			cache.set(target, pified);
+			return Reflect.apply(pified, thisArg, args);
+		},
+
+		get(target, key) {
+			const prop = target[key];
+
+			// eslint-disable-next-line no-use-extend-native/no-use-extend-native
+			if (!filter(target, key) || prop === Function.prototype[key]) {
+				return prop;
+			}
+
+			const cached = cache.get(prop);
+
+			if (cached) {
+				return cached;
+			}
+
+			if (typeof prop === 'function') {
+				const pified = processFn(prop, options, proxy, target);
+				cache.set(prop, pified);
+				return pified;
+			}
+
+			return prop;
+		}
+	});
 
-	return ret;
+	return proxy;
 };

package.json

@@ -43,7 +43,7 @@
 		"bluebird"
 	],
 	"devDependencies": {
-		"ava": "^0.25.0",
+		"ava": "^2.4.0",
 		"pinkie-promise": "^2.0.0",
 		"v8-natives": "^1.1.0",
 		"xo": "^0.23.0"

test.js

@@ -176,7 +176,7 @@ test('`errorFirst` option and `multiArgs`', async t => {
 	})('🦄', '🌈'), ['🦄', '🌈']);
 });
 
-test('class support - creates a copy', async t => {
+test('class support - does not create a copy', async t => {
 	const obj = {
 		x: 'foo',
 		y(cb) {
@@ -186,28 +186,17 @@ test('class support - creates a copy', async t => {
 		}
 	};
 
-	const pified = m(obj, {bind: false});
+	const pified = m(obj);
 	obj.x = 'bar';
 
-	t.is(await pified.y(), 'foo');
-	t.is(pified.x, 'foo');
+	t.is(await pified.y(), 'bar');
+	t.is(pified.x, 'bar');
 });
 
 test('class support — transforms inherited methods', t => {
 	const instance = new FixtureClass();
 	const pInstance = m(instance);
 
-	const flattened = {};
-	for (let prot = instance; prot; prot = Object.getPrototypeOf(prot)) {
-		Object.assign(flattened, prot);
-	}
-
-	const keys = Object.keys(flattened);
-	keys.sort();
-	const pKeys = Object.keys(pInstance);
-	pKeys.sort();
-	t.deepEqual(keys, pKeys);
-
 	t.is(instance.value1, pInstance.value1);
 	t.is(typeof pInstance.instanceMethod1().then, 'function');
 	t.is(typeof pInstance.method1().then, 'function');
@@ -236,17 +225,6 @@ test('class support - transforms only members in options.include, copies all', t
 		include: ['parentMethod1']
 	});
 
-	const flattened = {};
-	for (let prot = instance; prot; prot = Object.getPrototypeOf(prot)) {
-		Object.assign(flattened, prot);
-	}
-
-	const keys = Object.keys(flattened);
-	keys.sort();
-	const pKeys = Object.keys(pInstance);
-	pKeys.sort();
-	t.deepEqual(keys, pKeys);
-
 	t.is(typeof pInstance.parentMethod1().then, 'function');
 	t.not(typeof pInstance.method1(() => {}).then, 'function');
 	t.not(typeof pInstance.grandparentMethod1(() => {}).then, 'function');
@@ -278,3 +256,90 @@ test('promisify prototype function', async t => {
 	const instance = new FixtureClass();
 	t.is(await instance.method2Async(), 72);
 });
+
+test('method mutation', async t => {
+	const obj = {
+		foo(cb) {
+			setImmediate(() => cb(null, 'original'));
+		}
+	};
+	const pified = m(obj);
+
+	obj.foo = cb => setImmediate(() => cb(null, 'new'));
+
+	t.is(await pified.foo(), 'new');
+});
+
+test('symbol keys', async t => {
+	await t.notThrowsAsync(async () => {
+		const sym = Symbol('sym');
+		const obj = {[sym]: cb => setImmediate(cb)};
+		const pified = m(obj);
+		await pified[sym]();
+	});
+});
+
+// [[Get]] for proxy objects enforces the following invariants: The value
+// reported for a property must be the same as the value of the corresponding
+// target object property if the target object property is a non-writable,
+// non-configurable own data property.
+test('non-writable non-configurable property', t => {
+	const obj = {};
+	Object.defineProperty(obj, 'prop', {
+		value: cb => setImmediate(cb),
+		writable: false,
+		configurable: false
+	});
+
+	const pified = m(obj);
+	t.notThrows(() => Reflect.get(pified, 'prop'));
+});
+
+test('do not promisify Function.prototype.bind', async t => {
+	function fn(cb) {
+		cb(null, this);
+	}
+	const target = {};
+	t.is(await m(fn).bind(target)(), target);
+});
+
+test('do not break internal callback usage', async t => {
+	const obj = {
+		foo(cb) {
+			this.bar(4, cb);
+		},
+		bar(...args) {
+			const cb = args.pop();
+			cb(null, 42);
+		}
+	};
+	t.is(await m(obj).foo(), 42);
+});
+
+test('Function.prototype.call', async t => {
+	function fn(...args) {
+		const cb = args.pop();
+		cb(null, args.length);
+	}
+	const pified = m(fn);
+	t.is(await pified.call(), 0);
+});
+
+test('Function.prototype.apply', async t => {
+	function fn(...args) {
+		const cb = args.pop();
+		cb(null, args.length);
+	}
+	const pified = m(fn);
+	t.is(await pified.apply(), 0);
+});
+
+test('self as member', async t => {
+	function fn(...args) {
+		const cb = args.pop();
+		cb(null, args.length);
+	}
+	fn.self = fn;
+	const pified = m(fn);
+	t.is(await pified.self(), 0);
+});