From 4151ab398b8186f10056c4551edfa0204e529035 Mon Sep 17 00:00:00 2001
From: James M Snell <jasnell@gmail.com>
Date: Wed, 15 Feb 2017 07:43:22 -0800
Subject: [PATCH] util: add createClassWrapper to internal/util
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Utility function for wrapping an ES6 class with a constructor
function that does not require the new keyword

PR-URL: https://github.com/nodejs/node/pull/11391
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Sam Roberts <vieuxtech@gmail.com>
---
 lib/internal/util.js                          | 20 ++++++++++++
 .../test-internal-util-classwrapper.js        | 31 +++++++++++++++++++
 2 files changed, 51 insertions(+)
 create mode 100644 test/parallel/test-internal-util-classwrapper.js

diff --git a/lib/internal/util.js b/lib/internal/util.js
index 10844b645455dd..76ef759cefbc83 100644
--- a/lib/internal/util.js
+++ b/lib/internal/util.js
@@ -186,3 +186,23 @@ exports.toLength = function toLength(argument) {
   const len = toInteger(argument);
   return len <= 0 ? 0 : Math.min(len, Number.MAX_SAFE_INTEGER);
 };
+
+// Useful for Wrapping an ES6 Class with a constructor Function that
+// does not require the new keyword. For instance:
+//   class A { constructor(x) {this.x = x;}}
+//   const B = createClassWrapper(A);
+//   B() instanceof A // true
+//   B() instanceof B // true
+exports.createClassWrapper = function createClassWrapper(type) {
+  const fn = function(...args) {
+    return Reflect.construct(type, args, new.target || type);
+  };
+  // Mask the wrapper function name and length values
+  Object.defineProperties(fn, {
+    name: {value: type.name},
+    length: {value: type.length}
+  });
+  Object.setPrototypeOf(fn, type);
+  fn.prototype = type.prototype;
+  return fn;
+};
diff --git a/test/parallel/test-internal-util-classwrapper.js b/test/parallel/test-internal-util-classwrapper.js
new file mode 100644
index 00000000000000..52b3c2b0a9b50a
--- /dev/null
+++ b/test/parallel/test-internal-util-classwrapper.js
@@ -0,0 +1,31 @@
+// Flags: --expose-internals
+'use strict';
+
+require('../common');
+const assert = require('assert');
+const util = require('internal/util');
+
+const createClassWrapper = util.createClassWrapper;
+
+class A {
+  constructor(a, b, c) {
+    this.a = a;
+    this.b = b;
+    this.c = c;
+  }
+}
+
+const B = createClassWrapper(A);
+
+assert.strictEqual(typeof B, 'function');
+assert(B(1, 2, 3) instanceof B);
+assert(B(1, 2, 3) instanceof A);
+assert(new B(1, 2, 3) instanceof B);
+assert(new B(1, 2, 3) instanceof A);
+assert.strictEqual(B.name, A.name);
+assert.strictEqual(B.length, A.length);
+
+const b = new B(1, 2, 3);
+assert.strictEqual(b.a, 1);
+assert.strictEqual(b.b, 2);
+assert.strictEqual(b.c, 3);