Remove Error and make BufferSource checks realm-independent

The Error type has been removed from the Web IDL specification, so we can remove it here.

For the BufferSource types, we improve their checks to be realm-independent. Given jsdom's move to separate the Node.js globals from the JSDOM globals, instanceof being incorrect is now causing actual problems.

Helps with jsdom/jsdom#2743. Makes #12 slightly better, but there are still forgeable checks for the typed arrays, based on V.constructor.name.

Author: domenic

README.md

@@ -40,7 +40,6 @@ Conversions for all of the basic types from the Web IDL specification are implem
 - [`DOMString`](https://heycam.github.io/webidl/#es-DOMString), which can additionally be provided the boolean option `{ treatNullAsEmptyString }` as a second parameter
 - [`ByteString`](https://heycam.github.io/webidl/#es-ByteString), [`USVString`](https://heycam.github.io/webidl/#es-USVString)
 - [`object`](https://heycam.github.io/webidl/#es-object)
-- [`Error`](https://heycam.github.io/webidl/#es-Error)
 - [Buffer source types](https://heycam.github.io/webidl/#es-buffer-source-types)
 
 Additionally, for convenience, the following derived type definitions are implemented:
@@ -77,4 +76,4 @@ And getting to that payoff is the goal of _this_ project—but for JavaScript im
 
 Seriously, why would you ever use this? You really shouldn't. Web IDL is … strange, and you shouldn't be emulating its semantics. If you're looking for a generic argument-processing library, you should find one with better rules than those from Web IDL. In general, your JavaScript should not be trying to become more like Web IDL; if anything, we should fix Web IDL to make it more like JavaScript.
 
-The _only_ people who should use this are those trying to create faithful implementations (or polyfills) of web platform interfaces defined in Web IDL. Its main consumer is the [jsdom](https://github.com/tmpvar/jsdom) project.
+The _only_ people who should use this are those trying to create faithful implementations (or polyfills) of web platform interfaces defined in Web IDL. Its main consumer is the [jsdom](https://github.com/jsdom/jsdom) project.

lib/index.js

@@ -290,16 +290,45 @@ function convertCallbackFunction(V, opts) {
     return V;
 }
 
+const abByteLengthGetter =
+    Object.getOwnPropertyDescriptor(ArrayBuffer.prototype, "byteLength").get;
+
+function isArrayBuffer(V) {
+    try {
+        abByteLengthGetter.call(V);
+        return true;
+    } catch (e) {
+        return false;
+    }
+}
+
+// I don't think we can reliably detect detached ArrayBuffers.
+exports.ArrayBuffer = (V, opts) => {
+    if (!isArrayBuffer(V)) {
+        throw new TypeError(_("is not a view on an ArrayBuffer object", opts));
+    }
+    return V;
+};
+
+const dvByteLengthGetter =
+    Object.getOwnPropertyDescriptor(DataView.prototype, "byteLength").get;
+exports.DataView = (V, opts) => {
+    try {
+        dvByteLengthGetter.call(V);
+        return V;
+    } catch (e) {
+        throw new TypeError(_("is not a view on an DataView object", opts));
+    }
+};
+
 [
-    Error,
-    ArrayBuffer, // The IsDetachedBuffer abstract operation is not exposed in JS
-    DataView, Int8Array, Int16Array, Int32Array, Uint8Array,
+    Int8Array, Int16Array, Int32Array, Uint8Array,
     Uint16Array, Uint32Array, Uint8ClampedArray, Float32Array, Float64Array
 ].forEach(func => {
     const name = func.name;
     const article = /^[AEIOU]/.test(name) ? "an" : "a";
     exports[name] = (V, opts) => {
-        if (!(V instanceof func)) {
+        if (!ArrayBuffer.isView(V) || V.constructor.name !== name) {
             throw new TypeError(_(`is not ${article} ${name} object`, opts));
         }
 
@@ -318,7 +347,7 @@ exports.ArrayBufferView = (V, opts) => {
 };
 
 exports.BufferSource = (V, opts) => {
-    if (!(ArrayBuffer.isView(V) || V instanceof ArrayBuffer)) {
+    if (!ArrayBuffer.isView(V) && !isArrayBuffer(V)) {
         throw new TypeError(_("is not an ArrayBuffer object or a view on one", opts));
     }
 

test/buffer-source.js

@@ -1,5 +1,6 @@
 "use strict";
 const assert = require("assert");
+const vm = require("vm");
 
 const conversions = require("..");
 
@@ -62,11 +63,10 @@ function testNotOk(name, sut, create) {
     });
 }
 
-const bufferSourceCreators = [
-    { constructor: DataView, creator: () => new DataView(new ArrayBuffer(0)) }
-];
+const differentRealm = vm.createContext();
 
-[
+const bufferSourceConstructors = [
+    DataView,
     ArrayBuffer,
     Int8Array,
     Int16Array,
@@ -77,48 +77,55 @@ const bufferSourceCreators = [
     Uint8ClampedArray,
     Float32Array,
     Float64Array
-].forEach(constructor => {
-    bufferSourceCreators.push({ constructor, creator: () => new constructor(0) });
-});
+];
 
-bufferSourceCreators.forEach(type => {
-    const name = type.constructor.name;
-    const sut = conversions[name];
+const bufferSourceCreators = [];
+for (const constructor of bufferSourceConstructors) {
+    bufferSourceCreators.push(
+        {
+            typeName: constructor.name,
+            label: `${constructor.name} same realm`,
+            creator: () => new constructor(new ArrayBuffer(0))
+        },
+        {
+            typeName: constructor.name,
+            label: `${constructor.name} different realm`,
+            creator: () => vm.runInContext(`new ${constructor.name}(new ArrayBuffer(0))`, differentRealm)
+        }
+    );
+}
 
-    describe("WebIDL " + name + " type", () => {
-        bufferSourceCreators.forEach(innerType => {
-            const innerTypeName = innerType.constructor.name;
-            const create = innerType.creator;
+for (const type of bufferSourceConstructors) {
+    const typeName = type.name;
+    const sut = conversions[typeName];
 
-            (innerType === type ? testOk : testNotOk)(innerTypeName, sut, create);
-        });
+    describe("WebIDL " + typeName + " type", () => {
+        for (const innerType of bufferSourceCreators) {
+            const testFunction = innerType.typeName === typeName ? testOk : testNotOk;
+            testFunction(innerType.label, sut, innerType.creator);
+        }
 
         commonNotOk(sut);
     });
-});
+}
 
 describe("WebIDL ArrayBufferView type", () => {
     const sut = conversions.ArrayBufferView;
 
-    bufferSourceCreators.forEach(type => {
-        const name = type.constructor.name;
-        const create = type.creator;
-
-        (name === "ArrayBuffer" ? testNotOk : testOk)(name, sut, create);
-    });
+    for (const { label, typeName, creator } of bufferSourceCreators) {
+        const testFunction = typeName !== "ArrayBuffer" ? testOk : testNotOk;
+        testFunction(label, sut, creator);
+    }
 
     commonNotOk(sut);
 });
 
 describe("WebIDL BufferSource type", () => {
     const sut = conversions.BufferSource;
 
-    bufferSourceCreators.forEach(type => {
-        const name = type.constructor.name;
-        const create = type.creator;
-
-        testOk(name, sut, create);
-    });
+    for (const { label, creator } of bufferSourceCreators) {
+        testOk(label, sut, creator);
+    }
 
     commonNotOk(sut);
 });