8 files changed, 37 insertions, 0 deletions
diff --git a/js/custom_event.ts b/js/custom_event.ts
index 713794e28..5f9e413fb 100644
--- a/js/custom_event.ts
+++ b/js/custom_event.ts
@@ -52,6 +52,10 @@ export class CustomEvent extends event.Event implements domTypes.CustomEvent {
 
     customEventAttributes.set(this, { detail });
   }
+
+  get [Symbol.toStringTag](): string {
+    return "CustomEvent";
+  }
 }
 
 /** Built-in objects providing `get` methods for our
diff --git a/js/custom_event_test.ts b/js/custom_event_test.ts
index 20c901303..2f8f5c1a0 100644
--- a/js/custom_event_test.ts
+++ b/js/custom_event_test.ts
@@ -19,3 +19,9 @@ test(function customEventInitializedWithDetail() {
   assertEquals(event.target, null);
   assertEquals(event.type, type);
 });
+
+test(function toStringShouldBeWebCompatibility() {
+  const type = "touchstart";
+  const event = new CustomEvent(type, {});
+  assertEquals(event.toString(), "[object CustomEvent]");
+});
diff --git a/js/event_target.ts b/js/event_target.ts
index d6020ce7a..cc436865e 100644
--- a/js/event_target.ts
+++ b/js/event_target.ts
@@ -53,4 +53,8 @@ export class EventTarget implements domTypes.EventTarget {
     }
     return !event.defaultPrevented;
   }
+
+  get [Symbol.toStringTag](): string {
+    return "EventTarget";
+  }
 }
diff --git a/js/event_target_test.ts b/js/event_target_test.ts
index c1c9bb1f4..71c872dab 100644
--- a/js/event_target_test.ts
+++ b/js/event_target_test.ts
@@ -87,3 +87,8 @@ test(function constructedEventTargetUseObjectPrototype() {
   target.dispatchEvent(event);
   assertEquals(callCount, 2);
 });
+
+test(function toStringShouldBeWebCompatibility() {
+  const target = new EventTarget();
+  assertEquals(target.toString(), "[object EventTarget]");
+});
diff --git a/js/form_data.ts b/js/form_data.ts
index 3b3096785..1a8a72826 100644
--- a/js/form_data.ts
+++ b/js/form_data.ts
@@ -136,6 +136,10 @@ class FormDataBase {
       }
     }
   }
+
+  get [Symbol.toStringTag](): string {
+    return "FormData";
+  }
 }
 
 export class FormData extends DomIterableMixin<
diff --git a/js/form_data_test.ts b/js/form_data_test.ts
index bdf1e7cda..c02811fbc 100644
--- a/js/form_data_test.ts
+++ b/js/form_data_test.ts
@@ -166,3 +166,8 @@ test(function formDataParamsArgumentsCheck() {
     );
   });
 });
+
+test(function toStringShouldBeWebCompatibility() {
+  const formData = new FormData();
+  assertEquals(formData.toString(), "[object FormData]");
+});
diff --git a/js/headers.ts b/js/headers.ts
index dcb5f4c6a..2f15f14da 100644
--- a/js/headers.ts
+++ b/js/headers.ts
@@ -125,6 +125,10 @@ class HeadersBase {
     this._validateValue(newvalue);
     this[headerMap].set(newname, newvalue);
   }
+
+  get [Symbol.toStringTag](): string {
+    return "Headers";
+  }
 }
 
 // @internal
diff --git a/js/headers_test.ts b/js/headers_test.ts
index 4a911f9a5..2e6b48e88 100644
--- a/js/headers_test.ts
+++ b/js/headers_test.ts
@@ -316,3 +316,8 @@ test(function headerParamsArgumentsCheck() {
     );
   });
 });
+
+test(function toStringShouldBeWebCompatibility() {
+  const headers = new Headers();
+  assertEquals(headers.toString(), "[object Headers]");
+});