fix: change the condition within the Animal[Symbol.hasInstance] to match the purpose of the method #3682
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
Description
According to the comment above the
class Animal
, the purpose of theAnimal[Symbol.hasInstance]
method is to "assume that anything with the canEat property is an animal". The conditionif (obj.canEat) return true;
doesn't fit the purpose mentioned, because it checks whether!!obj.canEat === true
. So if we create the object with falsycanEat
property value (for example:let obj = { canEat: false};
), thenobj instanceof Animal
will returnfalse
, meaning thatobj
is not the instance ofAnimal
and the condition "anything with the canEat property is an animal" is not true.I suggest replacing the
if (obj.canEat) return true;
condition withif ('canEat' in obj) return true;
. Thein
operator returnstrue
if the specified property is in the specified object or its prototype chain. With the new condition,obj instanceof Animal
will returntrue
even if the value of thecanEat
property isfalse
, which is exactly the same as saying "anything with the canEat property is an animal".P.S. There is also a
hasOwnProperty()
method, which returns a boolean indicating whether this object has the specified property as its own property (as opposed to inheriting it). This method is not suitable for the implementationAnimal[Symbol.hasInstance]
, because the conditionif (obj.hasOwnProperty('canEat'))
will be truthy only if the propertycanEat
is a property of theobj
itself, but not of its prototypes.Links
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/in
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/hasOwnProperty