util: add createClassWrapper to internal/util

Utility function for wrapping an ES6 class with a constructor function that does not require the new keyword PR-URL: #11391 Reviewed-By: Michaël Zasso <[email protected]> Reviewed-By: Anna Henningsen <[email protected]> Reviewed-By: Sam Roberts <[email protected]>

Author: jasnell

lib/internal/util.js

@@ -186,3 +186,23 @@ exports.toLength = function toLength(argument){
 constlen=toInteger(argument);
 returnlen<=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=functioncreateClassWrapper(type){
+constfn=function(...args){
+returnReflect.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;
+returnfn;
+};

test/parallel/test-internal-util-classwrapper.js

@@ -0,0 +1,31 @@
+// Flags: --expose-internals
+'use strict';
+
+require('../common');
+constassert=require('assert');
+constutil=require('internal/util');
+
+constcreateClassWrapper=util.createClassWrapper;
+
+classA{
+constructor(a,b,c){
+this.a=a;
+this.b=b;
+this.c=c;
+}
+}
+
+constB=createClassWrapper(A);
+
+assert.strictEqual(typeofB,'function');
+assert(B(1,2,3)instanceofB);
+assert(B(1,2,3)instanceofA);
+assert(newB(1,2,3)instanceofB);
+assert(newB(1,2,3)instanceofA);
+assert.strictEqual(B.name,A.name);
+assert.strictEqual(B.length,A.length);
+
+constb=newB(1,2,3);
+assert.strictEqual(b.a,1);
+assert.strictEqual(b.b,2);
+assert.strictEqual(b.c,3);