Limited supportA good fit for shared utilities, cross-context error handling, and robust runtime validation.
Language core Limited support

Error.isError()

Error.isError() provides a reliable way to test whether a value is an Error instance. It is useful when instanceof checks become fragile across realms or execution contexts.

ErrorsValidationRuntime

Overview

Error.isError() provides a reliable way to test whether a value is an Error instance. It is useful when instanceof checks become fragile across realms or execution contexts.

Browser support

Feature Desktop Mobile
Chrome
Edge
Firefox
Safari
Chrome Android
Safari iOS
javascript.builtins.Error.isError
134
134
138
18.4
134
18.4
1+Supported (version) Not supported ※Has note Sub-feature descriptions sourced from MDN Web Docs (CC BY-SA 2.5)
Notes 2 item(s)
Limitation
  • This browser only partially implements this feature
Implementation note
  • Returns `false` for `DOMException` instances.
Notes 2 item(s)
Limitation
  • This browser only partially implements this feature
Implementation note
  • Returns `false` for `DOMException` instances.

Syntax

JAVASCRIPT 
Error.isError(new Error('test'));  // true
Error.isError(new TypeError());    // true
Error.isError({ message: 'fake' }); // false

Live demo

Check native Error objects

Use Error.isError when available, otherwise fall back to instanceof Error.

JavaScript
Output
Press the Run button

Inspect different thrown values

Compare errors, strings, and plain objects with the same helper.

JavaScript
Output
Press the Run button

Use inside catch handling

Normalize catch blocks that may receive non-Error values.

JavaScript
Output
Press the Run button

Use cases

  • Shared error pipelines

    Normalize error handling in utilities that may receive thrown values from different execution contexts.

  • Runtime guards

    Distinguish real Error objects from arbitrary thrown values before formatting or reporting them.

Cautions

  • A reliable error check still does not guarantee the value contains the information your UI needs.
  • Thrown strings and custom objects remain possible, so keep fallback handling in place.

Accessibility

  • Reliable error detection helps ensure users receive consistent failure messages and recovery options.
  • Error handling only improves accessibility if the resulting UI feedback is perceivable and actionable.

Related links

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