objhasOwnPropertypropertyName

hasOwnProperty is a method in JavaScript used to check whether a given object has a property as its own (not inherited through the prototype chain). It is defined on Object.prototype, so any object inherits it, but its result depends on whether the property exists directly on that object rather than on its prototype.

In practice, obj.hasOwnProperty(prop) returns true if obj has a direct property named prop. It returns false for properties that come from the prototype chain or for properties that are not present at all. The property key can be a string or a Symbol. A common caveat is that an object may override or shadow the hasOwnProperty method, which can lead to misleading results. To avoid this, a robust pattern is to call the method from Object.prototype directly: Object.prototype.hasOwnProperty.call(obj, prop).

Care is needed when obj is null or undefined, as calling hasOwnProperty on such values will throw a TypeError. A common safe check is to verify that the object is non-nullish before using the method, or to use a broader pattern that guards access: if (obj != null && Object.prototype.hasOwnProperty.call(obj, prop)) { ... }.

Since ES2022, a static method Object.hasOwn(obj, prop) provides a similar capability without relying on an object's own hasOwnProperty method. It returns true when obj has an own property named prop, and it throws if obj is not an object.

Overall, hasOwnProperty remains a fundamental tool for distinguishing direct properties from inherited ones, with a safe usage pattern and a modern, equivalent alternative available in Object.hasOwn.