Change the byob switch of ReadableStream constructor to a string swit…

…ch named type

Partially fixes #294

index.bs

@@ -422,7 +422,7 @@ Instances of {{ReadableStream}} are created with the internal slots described in
   state via the passed <code>controller</code> object. This is an example of the
   <a href="https://blog.domenic.me/the-revealing-constructor-pattern/">revealing constructor pattern</a>.
 
-  If the <code>underlyingSource</code> object contains a truthy property <code>byob</code>, this <a>readable stream</a> is
+  If the <code>underlyingSource</code> object contains a string property <code>type</code>, this <a>readable stream</a> is
   a <a>readable byte stream</a>, and can successfully vend <a>BYOB readers</a>. In that case, the passed
   <code>controller</code> object will be an instance of {{ReadableByteStreamController}}. Otherwise, it will be an instance of
   {{ReadableStreamDefaultController}}.
@@ -447,16 +447,18 @@ Instances of {{ReadableStream}} are created with the internal slots described in
   1. Set *this*@[[reader]] and *this*@[[storedError]] to *undefined*.
   1. Set *this*@[[disturbed]] to *false*.
   1. Set *this*@[[readableStreamController]] to *undefined*.
-  1. Let _byob_ be ToBoolean(GetV(_underlyingSource_, `"byob"`)).
-  1. ReturnIfAbrupt(_byob_).
-  1. If _byob_ is *true*,
+  1. Let _type_ be ToBoolean(GetV(_underlyingSource_, `"type"`)).
+  1. ReturnIfAbrupt(_type_).
+  1. If _type_ is `"bytes"`,
     1. If _highWaterMark_ is *undefined*,
       1. Let _highWaterMark_ be 0.
     1. Set *this*@[[readableStreamController]] to Construct(`<a idl>ReadableByteStreamController</a>`, «*this*, _underlyingSource_, _highWaterMark_»).
   1. Otherwise,
-    1. If _highWaterMark_ is *undefined*,
-      1. Let _highWaterMark_ be 1.
-    1. Set *this*@[[readableStreamController]] to Construct(`<a idl>ReadableStreamDefaultController</a>`, «*this*, _underlyingSource_, _size_, _highWaterMark_»).
+    1. If _type_ is *undefined*,
+      1. If _highWaterMark_ is *undefined*,
+        1. Let _highWaterMark_ be 1.
+      1. Set *this*@[[readableStreamController]] to Construct(`<a idl>ReadableStreamDefaultController</a>`, «*this*, _underlyingSource_, _size_, _highWaterMark_»).
+    1. Otherwise, throw a *TypeError* exception.
 </emu-alg>
 
 <h4 id="rs-prototype">Properties of the {{ReadableStream}} Prototype</h4>
@@ -3154,7 +3156,7 @@ BYOB reader, to move the data from the stream's internal queue to the developer-
     const socket = createHypotheticalSelect2Socket(host, port);
 
     return new ReadableStream({
-      byob: true,
+      type: "bytes",
 
       start(controller) {
         socket.setTCPWindowSize(Math.max(0, controller.desiredSize));
@@ -3261,7 +3263,7 @@ size of 1024, it attempts to fill the developer-supplied buffer, allowing full c
     let position = 0;
 
     return new ReadableStream({
-      byob: true,
+      type: "bytes",
 
       start() {
         return fs.open(filename, "r").then(result => {

reference-implementation/lib/readable-stream.js

@@ -22,17 +22,21 @@ export default class ReadableStream {
     // Initialize to undefined first because the constructor of the controller checks this
     // variable to validate the caller.
     this._readableStreamController = undefined;
-    const byob = underlyingSource['byob'];
-    if (byob === true) {
+    const type = underlyingSource['type'];
+    if (type === 'bytes') {
       if (highWaterMark === undefined) {
         highWaterMark = 0;
       }
       this._readableStreamController = new ReadableByteStreamController(this, underlyingSource, highWaterMark);
     } else {
-      if (highWaterMark === undefined) {
-        highWaterMark = 1;
+      if (type === undefined) {
+        if (highWaterMark === undefined) {
+          highWaterMark = 1;
+        }
+        this._readableStreamController = new ReadableStreamDefaultController(this, underlyingSource, size, highWaterMark);
+      } else {
+        throw new TypeError('Invalid type is specified');
       }
-      this._readableStreamController = new ReadableStreamDefaultController(this, underlyingSource, size, highWaterMark);
     }
   }