1 files changed, 123 insertions, 0 deletions
diff --git a/dom/streams/test/xpcshell/subclassing.js b/dom/streams/test/xpcshell/subclassing.js
new file mode 100644
index 0000000000..b2b86cf353
--- /dev/null
+++ b/dom/streams/test/xpcshell/subclassing.js
@@ -0,0 +1,123 @@
+// Adapted from js/src/tests/non262/ReadableStream/subclassing.js to suit requirements of xpcshell-testing.
+
+function assertEq(a, b) {
+  Assert.equal(a, b);
+}
+function assertThrowsInstanceOf(fun, err) {
+  var regexp = new RegExp(err.name);
+  print(regexp);
+  Assert.throws(fun, regexp);
+}
+
+// Spot-check subclassing of stream constructors.
+
+// ReadableStream can be subclassed.
+class PartyStreamer extends ReadableStream {}
+
+let started = false;
+add_task(function subclass_helper() {
+  // The base class constructor is called.
+  let stream = new PartyStreamer({
+    // (The ReadableStream constructor calls this start method.)
+    start(c) {
+      started = true;
+    },
+  });
+
+  assertEq(started, true);
+
+  // The instance's prototype chain is correct.
+  assertEq(stream.__proto__, PartyStreamer.prototype);
+  assertEq(stream.__proto__.__proto__, ReadableStream.prototype);
+  assertEq(stream.__proto__.__proto__.__proto__, Object.prototype);
+  assertEq(stream.__proto__.__proto__.__proto__.__proto__, null);
+  assertEq(stream instanceof ReadableStream, true);
+
+  // Non-generic methods can be called on the resulting stream.
+  stream.getReader();
+  assertEq(stream.locked, true);
+});
+
+add_task(function strategy_helper() {
+  // CountQueuingStrategy can be subclassed.
+  class PixelStrategy extends CountQueuingStrategy {}
+  assertEq(
+    new PixelStrategy({ highWaterMark: 4 }).__proto__,
+    PixelStrategy.prototype
+  );
+
+  // The base class constructor is called.
+  assertThrowsInstanceOf(() => new PixelStrategy(), TypeError);
+  assertEq(new PixelStrategy({ highWaterMark: -1 }).highWaterMark, -1);
+
+  // // VerySmartStrategy can be subclassed.
+  // class VerySmartStrategy extends ByteLengthQueuingStrategy {
+  //     size(chunk) {
+  //         return super.size(chunk) * 8;
+  //     }
+  // }
+  // let vss = new VerySmartStrategy({ highWaterMark: 12 });
+  // assertEq(vss.size(new ArrayBuffer(8)), 64);
+  // assertEq(vss.__proto__, VerySmartStrategy.prototype);
+});
+
+// Even ReadableStreamDefaultReader can be subclassed.
+add_task(async function readerTest() {
+  const ReadableStreamDefaultReader = new ReadableStream().getReader()
+    .constructor;
+  class MindReader extends ReadableStreamDefaultReader {
+    async read() {
+      let foretold = { value: "death", done: false };
+      let actual = await super.read();
+      actual = foretold; // ZOMG I WAS RIGHT, EXACTLY AS FORETOLD they should call me a righter
+      return actual;
+    }
+  }
+
+  let stream = new ReadableStream({
+    start(c) {
+      c.enqueue("one");
+      c.enqueue("two");
+    },
+    pull(c) {
+      c.close();
+    },
+  });
+  let reader = new MindReader(stream);
+  let result = await reader.read();
+  assertEq(result.value, "death");
+  reader.releaseLock();
+
+  reader = stream.getReader();
+  result = await reader.read();
+  assertEq(result.done, false);
+  assertEq(result.value, "two");
+  result = await reader.read();
+  assertEq(result.done, true);
+  assertEq(result.value, undefined);
+});
+
+add_task(function default_controller() {
+  // Even ReadableStreamDefaultController, which can't be constructed,
+  // can be subclassed.
+  let ReadableStreamDefaultController;
+  new ReadableStream({
+    start(c) {
+      ReadableStreamDefaultController = c.constructor;
+    },
+  });
+  class MasterController extends ReadableStreamDefaultController {
+    constructor() {
+      // don't call super, it'll just throw
+      return Object.create(MasterController.prototype);
+    }
+  }
+  let c = new MasterController();
+
+  // The prototype chain is per spec.
+  assertEq(c instanceof ReadableStreamDefaultController, true);
+
+  // But the instance does not have the internal slots of a
+  // ReadableStreamDefaultController, so the non-generic methods can't be used.
+  assertThrowsInstanceOf(() => c.enqueue("horse"), TypeError);
+});