Oct 14, 2025
diff --git a/1-js/09-classes/06-instanceof/article.md b/1-js/09-classes/06-instanceof/article.md
    alert(obj instanceof Animal); // true: Animal[Symbol.hasInstance](obj) is called
    ```

 ```smart header="Symbol.hasInstance can be in any ancestor class"
 If the constructor or one of its ancestors defines a custom static Symbol.hasInstance, the algorithm changes:
    1. It finds the nearest Symbol.hasInstance in the constructor inheritance chain and calls it.
    2. The return value of that Symbol.hasInstance determines the instanceof result.
 The default prototype chain comparison is not executed (regardless of the returned result).
 ```

    For example:

    ```js run
    class A {}

    class B extends A {
        static [Symbol.hasInstance](obj) {
            console.log('Custom "hasInstance" called');
            *!*
            return false;
            */!*
        }
    }
    class C extends B {}
    let c = new C();
    alert(c instanceof C); // false: B[Symbol.hasInstance](c) is called, and logs out 'Custom "hasInstance" called'
    ```

 2. Most classes do not have `Symbol.hasInstance`. In that case, the standard logic is used: `obj instanceof Class` checks whether `Class.prototype` is equal to one of the prototypes in the `obj` prototype chain.

    In other words, compare one after another:
Original file line number	Diff line number	Diff line change
Expand Up		@@ -68,6 +68,31 @@ The algorithm of `obj instanceof Class` works roughly as follows:
		alert(obj instanceof Animal); // true: Animal[Symbol.hasInstance](obj) is called
		```

		```smart header="Symbol.hasInstance can be in any ancestor class"
		If the constructor or one of its ancestors defines a custom static Symbol.hasInstance, the algorithm changes:
		1. It finds the nearest Symbol.hasInstance in the constructor inheritance chain and calls it.
		2. The return value of that Symbol.hasInstance determines the instanceof result.
		The default prototype chain comparison is not executed (regardless of the returned result).
		```

		For example:

		```js run
		class A {}

		class B extends A {
		static [Symbol.hasInstance](obj) {
		console.log('Custom "hasInstance" called');
		!
		return false;
		/!
		}
		}
		class C extends B {}
		let c = new C();
		alert(c instanceof C); // false: B[Symbol.hasInstance](c) is called, and logs out 'Custom "hasInstance" called'
		```

		2. Most classes do not have `Symbol.hasInstance`. In that case, the standard logic is used: `obj instanceof Class` checks whether `Class.prototype` is equal to one of the prototypes in the `obj` prototype chain.

		In other words, compare one after another:
Expand Down