My curiosity lies in understanding why the instanceof operator fails to work properly for the inheritance chain when there are multiple chains of inheritance involved.
(optional read)How does the
instanceofoperator function?When using
obj instanceof Constructor, theinstanceofoperator essentially checks if the'prototype'property of theConstructorfunction is found within the prototype chain of theobj. If it is found, true is returned; otherwise, false is returned.
In the code snippet below, we observe that BTError inherits from Error (1.) while SomeError extends from BTError (3.).
However, it appears that despite expectations (4.), the instanceof operation results in false for
new SomeError() instanceof BTErrortrue.
class BTError extends Error {}
console.log('1.', Reflect.getPrototypeOf(BTError.prototype) === Error.prototype); // 1. true
console.log('2.', new BTError() instanceof Error); // 2. true
console.log('');
class SomeError extends BTError {}
console.log('3.', Reflect.getPrototypeOf(SomeError.prototype) === BTError.prototype); // 3. true
console.log('4.', new SomeError() instanceof BTError); // 4. false
console.log('');
class SpecificError extends SomeError {}
console.log('5.', Reflect.getPrototypeOf(SpecificError.prototype) === SomeError.prototype); // 5. true
console.log('6.', new SpecificError() instanceof Error); // 6. true
console.log('7.', new SpecificError() instanceof BTError); // 7. false
console.log('8.', new SpecificError() instanceof SomeError); // 8. falseQuestion
Am I missing something significant here or is the behavior of the instanceof operator simply peculiar?