Implement “internally create a new object implementing the interface”

README.md

@@ -282,11 +282,11 @@ Creates a new instance of the wrapper class and corresponding implementation cla
 
 This is useful inside implementation class files, where it is easiest to only deal with impls, not wrappers.
 
-#### `new(globalObject)`
+#### `new(globalObject, newTarget)`
 
 Creates a new instance of the wrapper class and corresponding implementation class, but without invoking the implementation class constructor logic. Then returns the implementation class.
 
-This corresponds to the [Web IDL "new" algorithm](https://heycam.github.io/webidl/#new), and is useful when implementing specifications that initialize objects in different ways than their constructors do.
+This corresponds to the [WebIDL "create a new object implementing the interface"](https://heycam.github.io/webidl/#new) and ["internally create a new object implementing the interface"](https://heycam.github.io/webidl/#internally-create-a-new-object-implementing-the-interface) algorithms, and is useful when implementing specifications that initialize objects in different ways than their constructors do.
 
 #### `setup(obj, globalObject, constructorArgs, privateData)`
 

lib/constructs/interface.js

@@ -1194,17 +1194,25 @@ class Interface {
 
   generateIface() {
     this.str += `
-      function makeWrapper(globalObject) {
+      function makeWrapper(globalObject, newTarget) {
         if (globalObject[ctorRegistrySymbol] === undefined) {
           throw new Error('Internal error: invalid global object');
         }
 
-        const ctor = globalObject[ctorRegistrySymbol]["${this.name}"];
-        if (ctor === undefined) {
-          throw new Error('Internal error: constructor ${this.name} is not installed on the passed global object');
+        let proto;
+        if (newTarget !== undefined) {
+          proto = newTarget.prototype;
         }
 
-        return Object.create(ctor.prototype);
+        if (!utils.isObject(proto)) {
+          const ctor = globalObject[ctorRegistrySymbol]["${this.name}"];
+          if (ctor === undefined) {
+            throw new Error('Internal error: constructor ${this.name} is not installed on the passed global object');
+          }
+          proto = ctor.prototype;
+        }
+
+        return Object.create(proto);
       }
     `;
 
@@ -1272,8 +1280,8 @@ class Interface {
         return wrapper;
       };
 
-      exports.new = globalObject => {
-        ${this.isLegacyPlatformObj ? "let" : "const"} wrapper = makeWrapper(globalObject);
+      exports.new = (globalObject, newTarget) => {
+        ${this.isLegacyPlatformObj ? "let" : "const"} wrapper = makeWrapper(globalObject, newTarget);
 
         exports._internalSetup(wrapper, globalObject);
         Object.defineProperty(wrapper, implSymbol, {