stream: fix Writable instanceof for subclasses

addaleax · MylesBorins · commit 66187fa04450 · 2017-09-20T13:58:37.000-04:00
The current custom instanceof for `Writable` subclasses previously returned false positives for instances of *other* subclasses of `Writable` because it was inherited by these subclasses. Fixes: #14943 PR-URL: #14945 Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com> Reviewed-By: Refael Ackermann <refack@gmail.com> Reviewed-By: Timothy Gu <timothygu99@gmail.com> Reviewed-By: Colin Ihrig <cjihrig@gmail.com> Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de> Reviewed-By: Evan Lucas <evanlucas@me.com> Reviewed-By: James M Snell <jasnell@gmail.com>
diff --git a/lib/_stream_writable.js b/lib/_stream_writable.js
@@ -144,6 +144,8 @@ if (typeof Symbol === 'function' && Symbol.hasInstance) {
 value: function(object) {
 if (realHasInstance.call(this, object))
 return true;
+ if (this !== Writable)
+ return false;
 
 return object && object._writableState instanceof WritableState;
 }
diff --git a/test/parallel/test-stream-inheritance.js b/test/parallel/test-stream-inheritance.js
@@ -49,3 +49,8 @@ Object.setPrototypeOf(CustomWritable.prototype, Writable.prototype);
 new CustomWritable();
 
 assert.throws(CustomWritable, /AssertionError: undefined does not inherit from CustomWritable/);
+
+class OtherCustomWritable extends Writable {}
+
+assert(!(new OtherCustomWritable() instanceof CustomWritable));
+assert(!(new CustomWritable() instanceof OtherCustomWritable));

Original file line number	Diff line number	Diff line change
`@@ -144,6 +144,8 @@ if (typeof Symbol === 'function' && Symbol.hasInstance) {`
`144`	`144`	`value: function(object){`
`145`	`145`	`if(realHasInstance.call(this,object))`
`146`	`146`	`returntrue;`
	`147`	`+if(this!==Writable)`
	`148`	`+returnfalse;`
`147`	`149`
`148`	`150`	`returnobject&&object._writableStateinstanceofWritableState;`
`149`	`151`	`}`
-Original file line number
+Diff line change
 newCustomWritable();
 assert.throws(CustomWritable,/AssertionError:undefineddoesnotinheritfromCustomWritable/);
++
 +classOtherCustomWritableextendsWritable{}
++
 +assert(!(newOtherCustomWritable()instanceofCustomWritable));
 +assert(!(newCustomWritable()instanceofOtherCustomWritable));