syscall/js: add Value.Delete for deleting JavaScript properties

This change adds the method Value.Delete, which implements
JavaScript's "delete" operator for deleting properties.

Fixes #33079.

Change-Id: Ia5b190240bd59daca48094fcbc32f8d0a06f19d5
Reviewed-on: https://go-review.googlesource.com/c/go/+/197840
Run-TryBot: Richard Musiol <neelance@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>

misc/wasm/wasm_exec.js

@@ -308,6 +308,11 @@
 						Reflect.set(loadValue(sp + 8), loadString(sp + 16), loadValue(sp + 32));
 					},
 
+					// func valueDelete(v ref, p string)
+					"syscall/js.valueDelete": (sp) => {
+						Reflect.deleteProperty(loadValue(sp + 8), loadString(sp + 16));
+					},
+
 					// func valueIndex(v ref, i int) ref
 					"syscall/js.valueIndex": (sp) => {
 						storeValue(sp + 24, Reflect.get(loadValue(sp + 8), getInt64(sp + 16)));

src/syscall/js/js.go

@@ -267,6 +267,17 @@ func (v Value) Set(p string, x interface{}) {
 
 func valueSet(v ref, p string, x ref)
 
+// Delete deletes the JavaScript property p of value v.
+// It panics if v is not a JavaScript object.
+func (v Value) Delete(p string) {
+	if vType := v.Type(); !vType.isObject() {
+		panic(&ValueError{"Value.Delete", vType})
+	}
+	valueDelete(v.ref, p)
+}
+
+func valueDelete(v ref, p string)
+
 // Index returns JavaScript index i of value v.
 // It panics if v is not a JavaScript object.
 func (v Value) Index(i int) Value {

src/syscall/js/js_js.s

@@ -16,6 +16,10 @@ TEXT ·valueSet(SB), NOSPLIT, $0
   CallImport
   RET
 
+TEXT ·valueDelete(SB), NOSPLIT, $0
+  CallImport
+  RET
+
 TEXT ·valueIndex(SB), NOSPLIT, $0
   CallImport
   RET

src/syscall/js/js_test.go

@@ -212,6 +212,18 @@ func TestSet(t *testing.T) {
 	})
 }
 
+func TestDelete(t *testing.T) {
+	dummys.Set("test", 42)
+	dummys.Delete("test")
+	if dummys.Call("hasOwnProperty", "test").Bool() {
+		t.Errorf("property still exists")
+	}
+
+	expectValueError(t, func() {
+		dummys.Get("zero").Delete("badField")
+	})
+}
+
 func TestIndex(t *testing.T) {
 	if got := dummys.Get("someArray").Index(1).Int(); got != 42 {
 		t.Errorf("got %#v, want %#v", got, 42)