invalid_runtime_check_with_js_interop_types

Cast from '{0}' to '{1}' casts a Dart value to a JS interop type, which might not be platform-consistent.

Cast from '{0}' to '{1}' casts a JS interop value to a Dart type, which might not be platform-consistent.

Cast from '{0}' to '{1}' casts a JS interop value to an incompatible JS interop type, which might not be platform-consistent.

Runtime check between '{0}' and '{1}' checks whether a Dart value is a JS interop type, which might not be platform-consistent.

Runtime check between '{0}' and '{1}' checks whether a JS interop value is a Dart type, which might not be platform-consistent.

Runtime check between '{0}' and '{1}' involves a non-trivial runtime check between two JS interop types that might not be platform-consistent.

Runtime check between '{0}' and '{1}' involves a runtime check between a JS interop value and an unrelated JS interop type that will always be true and won't check the underlying type.

The analyzer produces this diagnostic when an is test has either:

• a JS interop type on the right-hand side, whether directly or as a type argument to another type, or
• a JS interop value on the left-hand side.

The following code produces this diagnostic because the JS interop type JSBoolean is on the right-hand side of an is test:

import 'dart:js_interop';

bool f(Object b) => b is JSBoolean;

The following code produces this diagnostic because the JS interop type JSString is used as a type argument on the right-hand side of an is test:

import 'dart:js_interop';

bool f(List<Object> l) => l is List<JSString>;

The following code produces this diagnostic because the JS interop value a is on the left-hand side of an is test:

import 'dart:js_interop';

bool f(JSAny a) => a is String;

Use a JS interop helper, such as isA, to check the underlying type of JS interop values:

import 'dart:js_interop';

void f(Object b) => b.jsify()?.isA<JSBoolean>();

Unless stated otherwise, the documentation on this site reflects Dart 3.7.3. Page last updated on 2025-05-08. View source or report an issue.