isError()

isError(value): value is Error

Checks if a value is an Error instance.

note

Also returns true for Error subclasses (TypeError, RangeError, custom errors).

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Parameters

value: unknown

The value to check.

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Returns: value is Error

true if the value is an Error, false otherwise.

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Since

2.0.0

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Example

isError(new Error('oops'));     // => true
isError(new TypeError('bad'));  // => true
isError({ message: 'fake' });   // => false
isError('error string');        // => false

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How it works?

Type guard that checks if a value is an Error instance.

Type Narrowing

Common Checks

Value	Result
new Error('msg')	true
new TypeError('msg')	true
new RangeError('msg')	true
new SyntaxError('msg')	true
{ message: 'error' }	false
'Error'	false

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Use Cases

Catch exceptions correctly 📌

Distinguish between standard Error objects and other thrown values. Critical for robust error handling and logging.

#catch#exceptions#errors#handling#logging#debugging

try {
  dangerousCall();
} catch (err) {
  if (isError(err)) {
    logError(err.message, err.stack);
  }
}