3 files changed, 84 insertions, 4 deletions
diff --git a/cli/js/web/streams/internals.ts b/cli/js/web/streams/internals.ts
index 5ef094afc..e2e7bbc0a 100644
--- a/cli/js/web/streams/internals.ts
+++ b/cli/js/web/streams/internals.ts
@@ -140,7 +140,7 @@ function createReadableStream<T>(
   highWaterMark = 1,
   sizeAlgorithm: SizeAlgorithm<T> = (): number => 1
 ): ReadableStreamImpl<T> {
-  assert(isNonNegativeNumber(highWaterMark));
+  highWaterMark = validateAndNormalizeHighWaterMark(highWaterMark);
   const stream: ReadableStreamImpl<T> = Object.create(
     ReadableStreamImpl.prototype
   );
@@ -168,7 +168,7 @@ function createWritableStream<W>(
   highWaterMark = 1,
   sizeAlgorithm: SizeAlgorithm<W> = (): number => 1
 ): WritableStreamImpl<W> {
-  assert(isNonNegativeNumber(highWaterMark));
+  highWaterMark = validateAndNormalizeHighWaterMark(highWaterMark);
   const stream = Object.create(WritableStreamImpl.prototype);
   initializeWritableStream(stream);
   const controller = Object.create(
@@ -324,7 +324,7 @@ function isNonNegativeNumber(v: unknown): v is number {
   if (typeof v !== "number") {
     return false;
   }
-  if (v === NaN) {
+  if (Number.isNaN(v)) {
     return false;
   }
   if (v < 0) {
@@ -1872,7 +1872,7 @@ export function validateAndNormalizeHighWaterMark(
   highWaterMark: number
 ): number {
   highWaterMark = Number(highWaterMark);
-  if (highWaterMark === NaN || highWaterMark < 0) {
+  if (Number.isNaN(highWaterMark) || highWaterMark < 0) {
     throw new RangeError(
       `highWaterMark must be a positive number or Infinity.  Received: ${highWaterMark}.`
     );
diff --git a/cli/tests/unit/streams_internal_test.ts b/cli/tests/unit/streams_internal_test.ts
new file mode 100644
index 000000000..f324da194
--- /dev/null
+++ b/cli/tests/unit/streams_internal_test.ts
@@ -0,0 +1,79 @@
+// Copyright 2018-2020 the Deno authors. All rights reserved. MIT license.
+import { unitTest, assertThrows } from "./test_util.ts";
+
+unitTest(function streamReadableHwmError() {
+  const invalidHwm = [NaN, Number("NaN"), {}, -1, "two"];
+  for (const highWaterMark of invalidHwm) {
+    assertThrows(
+      () => {
+        new ReadableStream<number>(
+          undefined,
+          // @ts-ignore
+          { highWaterMark }
+        );
+      },
+      RangeError,
+      "highWaterMark must be a positive number or Infinity.  Received:"
+    );
+  }
+
+  assertThrows(() => {
+    new ReadableStream<number>(
+      undefined,
+      // @ts-ignore
+      { highWaterMark: Symbol("hwk") }
+    );
+  }, TypeError);
+});
+
+unitTest(function streamWriteableHwmError() {
+  const invalidHwm = [NaN, Number("NaN"), {}, -1, "two"];
+  for (const highWaterMark of invalidHwm) {
+    assertThrows(
+      () => {
+        new WritableStream(
+          undefined,
+          // @ts-ignore
+          new CountQueuingStrategy({ highWaterMark })
+        );
+      },
+      RangeError,
+      "highWaterMark must be a positive number or Infinity.  Received:"
+    );
+  }
+
+  assertThrows(() => {
+    new WritableStream(
+      undefined,
+      // @ts-ignore
+      new CountQueuingStrategy({ highWaterMark: Symbol("hwmk") })
+    );
+  }, TypeError);
+});
+
+unitTest(function streamTransformHwmError() {
+  const invalidHwm = [NaN, Number("NaN"), {}, -1, "two"];
+  for (const highWaterMark of invalidHwm) {
+    assertThrows(
+      () => {
+        new TransformStream(
+          undefined,
+          undefined,
+          // @ts-ignore
+          { highWaterMark }
+        );
+      },
+      RangeError,
+      "highWaterMark must be a positive number or Infinity.  Received:"
+    );
+  }
+
+  assertThrows(() => {
+    new TransformStream(
+      undefined,
+      undefined,
+      // @ts-ignore
+      { highWaterMark: Symbol("hwmk") }
+    );
+  }, TypeError);
+});
diff --git a/cli/tests/unit/unit_tests.ts b/cli/tests/unit/unit_tests.ts
index 7327bcc05..515da9f4a 100644
--- a/cli/tests/unit/unit_tests.ts
+++ b/cli/tests/unit/unit_tests.ts
@@ -52,6 +52,7 @@ import "./request_test.ts";
 import "./resources_test.ts";
 import "./signal_test.ts";
 import "./stat_test.ts";
+import "./streams_internal_test.ts";
 import "./streams_piping_test.ts";
 import "./streams_transform_test.ts";
 import "./streams_writable_test.ts";