[dart2wasm] Implement == for JSValue.

Change-Id: I45af5bdabfb0dfa12b6b39094843b9394f4fe510
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/257923
Reviewed-by: Srujan Gaddam <srujzs@google.com>
Commit-Queue: Joshua Litt <joshualitt@google.com>

pkg/dart2wasm/bin/run_wasm.js

@@ -354,6 +354,9 @@ var dart2wasm = {
         }
         return stringToDartString(jsString);
     },
+    areEqualInJS: function(l, r) {
+        return l === r;
+    },
 };
 
 function instantiate(filename, imports) {

sdk/lib/_internal/wasm/lib/js_helper.dart

@@ -24,6 +24,10 @@ class JSValue {
   static JSValue? box(WasmAnyRef? ref) =>
       isDartNull(ref) ? null : JSValue(ref!);
 
+  @override
+  bool operator ==(Object that) =>
+      that is JSValue && areEqualInJS(_ref, that._ref);
+
   WasmAnyRef toAnyRef() => _ref;
   String toString() => jsStringToDartString(_ref);
   List<Object?> toObjectList() => toDartList(_ref);
@@ -196,6 +200,9 @@ external bool isJSSimpleObject(WasmAnyRef? o);
 @pragma("wasm:import", "dart2wasm.isJSRegExp")
 external bool isJSRegExp(WasmAnyRef object);
 
+@pragma("wasm:import", "dart2wasm.areEqualInJS")
+external bool areEqualInJS(WasmAnyRef? l, WasmAnyRef? r);
+
 // The JS runtime will run helpful conversion routines between refs and bool /
 // double. In the longer term hopefully we can find a way to avoid the round
 // trip.

tests/web/wasm/js_util_test.dart

@@ -19,6 +19,48 @@ void createObjectTest() {
   Expect.equals('bar', getProperty(o, 'foo'));
 }
 
+void equalTest() {
+  // Different objects aren't equal.
+  {
+    Object o1 = newObject();
+    Object o2 = newObject();
+    Expect.notEquals(o1, o2);
+  }
+
+  {
+    eval(r'''
+      function JSClass() {}
+
+      globalThis.boolData = true;
+      globalThis.boolData2 = true;
+      globalThis.numData = 4;
+      globalThis.numData2 = 4;
+      globalThis.arrData = [1, 2, 3];
+      globalThis.strData = 'foo';
+      globalThis.strData2 = 'foo';
+      globalThis.funcData = function JSClass() {}
+      globalThis.JSClass = new globalThis.funcData();
+    ''');
+    Object gt = globalThis;
+    void test(String propertyName, bool testCanonicalization) {
+      Expect.equals(
+          getProperty(gt, propertyName), getProperty(gt, propertyName));
+      if (testCanonicalization) {
+        Expect.equals(
+            getProperty(gt, propertyName), getProperty(gt, propertyName + "2"));
+      }
+    }
+
+    test("boolData", true);
+    test("numData", true);
+    // TODO(joshualitt): Start returning arrays by reference.
+    //test("arrData", false);
+    test("strData", true);
+    test("funcData", false);
+    test("JSClass", false);
+  }
+}
+
 void _expectIterableEquals(Iterable<Object?> l, Iterable<Object?> r) {
   final lIt = l.iterator;
   final rIt = r.iterator;
@@ -212,6 +254,7 @@ void deepConversionsTest() {
 
 void main() {
   createObjectTest();
+  equalTest();
   evalAndConstructTest();
   dartObjectRoundTripTest();
   deepConversionsTest();