misc/wasm: make sure value ref id is unique

For each Javascript object that returns to Go as a js.Value, we
associate the ref id to it. But if this ref id is copied or
inherited to other object, it would mess up the ref-object
mapping.

In storeValue, make sure the object is indeed the one we are
storing. Otherwise allocate a new ref id.

Fixes #26143.

Change-Id: Ie60bb2f8d1533da1bbe6f46045866515ec2af5a9
Reviewed-on: https://go-review.googlesource.com/121835
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Richard Musiol <neelance@gmail.com>

misc/wasm/wasm_exec.js

@@ -141,7 +141,7 @@
 				}
 
 				let ref = v[this._refProp];
-				if (ref === undefined) {
+				if (ref === undefined || this._values[ref] !== v) {
 					ref = this._values.length;
 					this._values.push(v);
 					v[this._refProp] = ref;

src/syscall/js/js_test.go

@@ -107,6 +107,13 @@ func TestObject(t *testing.T) {
 	if dummys.Get("someArray") != dummys.Get("someArray") {
 		t.Errorf("same value not equal")
 	}
+
+	// An object and its prototype should not be equal.
+	proto := js.Global().Get("Object").Get("prototype")
+	o := js.Global().Call("eval", "new Object()")
+	if proto == o {
+		t.Errorf("object equals to its prototype")
+	}
 }
 
 func TestTypedArrayOf(t *testing.T) {