getNativeArg: return a TypeError if js value is not an object

src/engines/v8/generate.zig

@@ -22,6 +22,10 @@ const TPL = @import("v8.zig").TPL;
 // Utils functions
 // ---------------
 
+const JSError = error{
+    InvalidArgument,
+};
+
 fn throwBasicError(msg: []const u8, isolate: v8.Isolate) v8.Value {
     const except_msg = v8.String.initUtf8(isolate, msg);
     const exception = v8.Exception.initError(except_msg);
@@ -36,6 +40,11 @@ fn throwError(
     err: anyerror,
     isolate: v8.Isolate,
 ) v8.Value {
+    // well known error.
+    switch (err) {
+        JSError.InvalidArgument => return throwTypeError("invalid argument", isolate),
+        else => {},
+    }
     const ret = func.return_type;
 
     // Is the returned Type a custom Exception error?
@@ -136,10 +145,9 @@ fn getNativeArg(
         if (comptime arg_T.underOpt() != null) {
             return null;
         }
-        // TODO: else return error "Argument x is not an object"
     }
 
-    if (!js_value.isObject()) unreachable; // TODO: throw js exception
+    if (!js_value.isObject()) return JSError.InvalidArgument;
 
     // JS object
     const ptr = getNativeObject(

src/tests/types_native_test.zig

@@ -293,8 +293,7 @@ pub fn exec(
     // not.
     // https://github.com/lightpanda-io/jsruntime-lib/issues/185
     var bug_native_obj = [_]tests.Case{
-        .{ .src = "let car = new Car();", .ex = "undefined" },
-        .{ .src = "car.changeBrand('foo');", .ex = "true" },
+        .{ .src = "try { car.changeBrand('foo'); false; } catch(e) { e instanceof TypeError; }", .ex = "true" },
     };
     try tests.checkCases(js_env, &bug_native_obj);
 }