diff --git a/src/browser/js/Caller.zig b/src/browser/js/Caller.zig
index cd4d25d3..ed4a4119 100644
--- a/src/browser/js/Caller.zig
+++ b/src/browser/js/Caller.zig
@@ -39,9 +39,22 @@ prev_local: ?*const js.Local,
 prev_context: *Context,
 
 // Takes the raw v8 isolate and extracts the context from it.
-pub fn init(self: *Caller, v8_isolate: *v8.Isolate) void {
-    const ctx, const v8_context = Context.fromIsolate(.{ .handle = v8_isolate });
+// Returns false if the context has been destroyed (e.g., navigated-away iframe),
+// in which case a JS exception has been thrown and the caller should return immediately.
+pub fn init(self: *Caller, v8_isolate: *v8.Isolate) bool {
+    const ctx, const v8_context = Context.fromIsolate(.{ .handle = v8_isolate }) orelse {
+        throwDetachedError(v8_isolate);
+        return false;
+    };
     initWithContext(self, ctx, v8_context);
+    return true;
+}
+
+fn throwDetachedError(isolate: *v8.Isolate) void {
+    const message = "Cannot execute in detached context (e.g., navigated-away iframe)";
+    const v8_message = v8.v8__String__NewFromUtf8(isolate, message.ptr, v8.kNormal, @intCast(message.len));
+    const js_exception = v8.v8__Exception__Error(v8_message);
+    _ = v8.v8__Isolate__ThrowException(isolate, js_exception);
 }
 
 fn initWithContext(self: *Caller, ctx: *Context, v8_context: *const v8.Context) void {
@@ -60,9 +73,9 @@ fn initWithContext(self: *Caller, ctx: *Context, v8_context: *const v8.Context)
     ctx.local = &self.local;
 }
 
-pub fn initFromHandle(self: *Caller, handle: ?*const v8.FunctionCallbackInfo) void {
+pub fn initFromHandle(self: *Caller, handle: ?*const v8.FunctionCallbackInfo) bool {
     const isolate = v8.v8__FunctionCallbackInfo__GetIsolate(handle).?;
-    self.init(isolate);
+    return self.init(isolate);
 }
 
 pub fn deinit(self: *Caller) void {
@@ -538,7 +551,10 @@ pub const Function = struct {
 
     pub fn call(comptime T: type, info_handle: *const v8.FunctionCallbackInfo, func: anytype, comptime opts: Opts) void {
         const v8_isolate = v8.v8__FunctionCallbackInfo__GetIsolate(info_handle).?;
-        const ctx, const v8_context = Context.fromIsolate(.{ .handle = v8_isolate });
+        const ctx, const v8_context = Context.fromIsolate(.{ .handle = v8_isolate }) orelse {
+            throwDetachedError(v8_isolate);
+            return;
+        };
         const info = FunctionCallbackInfo{ .handle = info_handle };
 
         var hs: js.HandleScope = undefined;
diff --git a/src/browser/js/Context.zig b/src/browser/js/Context.zig
index beec0625..b691af95 100644
--- a/src/browser/js/Context.zig
+++ b/src/browser/js/Context.zig
@@ -138,7 +138,8 @@ pub fn fromC(c_context: *const v8.Context) ?*Context {
 /// Returns the Context and v8::Context for the given isolate.
 /// If the current context is from a destroyed Context (e.g., navigated-away iframe),
 /// falls back to the incumbent context (the calling context).
-pub fn fromIsolate(isolate: js.Isolate) struct { *Context, *const v8.Context } {
+/// Returns null if neither context has a valid Context struct (both were destroyed).
+pub fn fromIsolate(isolate: js.Isolate) ?struct { *Context, *const v8.Context } {
     const v8_context = v8.v8__Isolate__GetCurrentContext(isolate.handle).?;
     if (fromC(v8_context)) |ctx| {
         return .{ ctx, v8_context };
@@ -146,7 +147,8 @@ pub fn fromIsolate(isolate: js.Isolate) struct { *Context, *const v8.Context } {
     // The current context's Context struct has been freed (e.g., iframe navigated away).
     // Fall back to the incumbent context (the calling context).
     const v8_incumbent = v8.v8__Isolate__GetIncumbentContext(isolate.handle).?;
-    return .{ fromC(v8_incumbent).?, v8_incumbent };
+    const ctx = fromC(v8_incumbent) orelse return null;
+    return .{ ctx, v8_incumbent };
 }
 
 pub fn deinit(self: *Context) void {
@@ -806,7 +808,9 @@ fn resolveDynamicModule(self: *Context, state: *DynamicModuleResolveState, modul
     const then_callback = newFunctionWithData(local, struct {
         pub fn callback(callback_handle: ?*const v8.FunctionCallbackInfo) callconv(.c) void {
             var c: Caller = undefined;
-            c.initFromHandle(callback_handle);
+            if (!c.initFromHandle(callback_handle)) {
+                return;
+            }
             defer c.deinit();
 
             const info = Caller.FunctionCallbackInfo{ .handle = callback_handle.? };
@@ -830,7 +834,7 @@ fn resolveDynamicModule(self: *Context, state: *DynamicModuleResolveState, modul
     const catch_callback = newFunctionWithData(local, struct {
         pub fn callback(callback_handle: ?*const v8.FunctionCallbackInfo) callconv(.c) void {
             var c: Caller = undefined;
-            c.initFromHandle(callback_handle);
+            if (!c.initFromHandle(callback_handle)) return;
             defer c.deinit();
 
             const info = Caller.FunctionCallbackInfo{ .handle = callback_handle.? };
diff --git a/src/browser/js/Env.zig b/src/browser/js/Env.zig
index bae6a8f0..2c1ebf38 100644
--- a/src/browser/js/Env.zig
+++ b/src/browser/js/Env.zig
@@ -519,7 +519,7 @@ fn promiseRejectCallback(message_handle: v8.PromiseRejectMessage) callconv(.c) v
     const promise_handle = v8.v8__PromiseRejectMessage__GetPromise(&message_handle).?;
     const v8_isolate = v8.v8__Object__GetIsolate(@ptrCast(promise_handle)).?;
     const isolate = js.Isolate{ .handle = v8_isolate };
-    const ctx, const v8_context = Context.fromIsolate(isolate);
+    const ctx, const v8_context = Context.fromIsolate(isolate) orelse return;
 
     const local = js.Local{
         .ctx = ctx,
diff --git a/src/browser/js/bridge.zig b/src/browser/js/bridge.zig
index 8fbdc315..93c51f78 100644
--- a/src/browser/js/bridge.zig
+++ b/src/browser/js/bridge.zig
@@ -116,7 +116,9 @@ pub const Constructor = struct {
             fn wrap(handle: ?*const v8.FunctionCallbackInfo) callconv(.c) void {
                 const v8_isolate = v8.v8__FunctionCallbackInfo__GetIsolate(handle).?;
                 var caller: Caller = undefined;
-                caller.init(v8_isolate);
+                if (!caller.init(v8_isolate)) {
+                    return;
+                }
                 defer caller.deinit();
 
                 caller.constructor(T, func, handle.?, .{
@@ -216,7 +218,9 @@ pub const Indexed = struct {
                 fn wrap(idx: u32, handle: ?*const v8.PropertyCallbackInfo) callconv(.c) u8 {
                     const v8_isolate = v8.v8__PropertyCallbackInfo__GetIsolate(handle).?;
                     var caller: Caller = undefined;
-                    caller.init(v8_isolate);
+                    if (!caller.init(v8_isolate)) {
+                        return 0;
+                    }
                     defer caller.deinit();
 
                     return caller.getIndex(T, getter, idx, handle.?, .{
@@ -232,7 +236,9 @@ pub const Indexed = struct {
                 fn wrap(handle: ?*const v8.PropertyCallbackInfo) callconv(.c) u8 {
                     const v8_isolate = v8.v8__PropertyCallbackInfo__GetIsolate(handle).?;
                     var caller: Caller = undefined;
-                    caller.init(v8_isolate);
+                    if (!caller.init(v8_isolate)) {
+                        return 0;
+                    }
                     defer caller.deinit();
                     return caller.getEnumerator(T, enumerator, handle.?, .{});
                 }
@@ -258,7 +264,9 @@ pub const NamedIndexed = struct {
             fn wrap(c_name: ?*const v8.Name, handle: ?*const v8.PropertyCallbackInfo) callconv(.c) u8 {
                 const v8_isolate = v8.v8__PropertyCallbackInfo__GetIsolate(handle).?;
                 var caller: Caller = undefined;
-                caller.init(v8_isolate);
+                if (!caller.init(v8_isolate)) {
+                    return 0;
+                }
                 defer caller.deinit();
 
                 return caller.getNamedIndex(T, getter, c_name.?, handle.?, .{
@@ -272,7 +280,9 @@ pub const NamedIndexed = struct {
             fn wrap(c_name: ?*const v8.Name, c_value: ?*const v8.Value, handle: ?*const v8.PropertyCallbackInfo) callconv(.c) u8 {
                 const v8_isolate = v8.v8__PropertyCallbackInfo__GetIsolate(handle).?;
                 var caller: Caller = undefined;
-                caller.init(v8_isolate);
+                if (!caller.init(v8_isolate)) {
+                    return 0;
+                }
                 defer caller.deinit();
 
                 return caller.setNamedIndex(T, setter, c_name.?, c_value.?, handle.?, .{
@@ -286,7 +296,9 @@ pub const NamedIndexed = struct {
             fn wrap(c_name: ?*const v8.Name, handle: ?*const v8.PropertyCallbackInfo) callconv(.c) u8 {
                 const v8_isolate = v8.v8__PropertyCallbackInfo__GetIsolate(handle).?;
                 var caller: Caller = undefined;
-                caller.init(v8_isolate);
+                if (!caller.init(v8_isolate)) {
+                    return 0;
+                }
                 defer caller.deinit();
 
                 return caller.deleteNamedIndex(T, deleter, c_name.?, handle.?, .{
@@ -387,7 +399,9 @@ pub const Property = struct {
 pub fn unknownWindowPropertyCallback(c_name: ?*const v8.Name, handle: ?*const v8.PropertyCallbackInfo) callconv(.c) u8 {
     const v8_isolate = v8.v8__PropertyCallbackInfo__GetIsolate(handle).?;
     var caller: Caller = undefined;
-    caller.init(v8_isolate);
+    if (!caller.init(v8_isolate)) {
+        return 0;
+    }
     defer caller.deinit();
 
     const local = &caller.local;
@@ -465,7 +479,9 @@ pub fn unknownObjectPropertyCallback(comptime JsApi: type) *const fn (?*const v8
             const v8_isolate = v8.v8__PropertyCallbackInfo__GetIsolate(handle).?;
 
             var caller: Caller = undefined;
-            caller.init(v8_isolate);
+            if (!caller.init(v8_isolate)) {
+                return 0;
+            }
             defer caller.deinit();
 
             const local = &caller.local;