Function hasOwnProperty

The objHasOwnProperty() method returns a boolean indicating whether the object has the specified property as its own property (as opposed to inheriting it).

The objHasOwnProperty() method returns true if the specified property is a direct property of the object — even if the value is null or undefined. The method returns false if the property is inherited, or has not been declared at all. Unlike the in operator, this method does not check for the specified property in the object's prototype chain.

The method can be called on most JavaScript objects, because most objects descend from Object, and hence inherit its methods. For example Array is an Object, so you can use objHasOwnProperty() method to check whether an index exists:

let example = {};
objHasOwnProperty(example, 'prop');   // false

example.prop = 'exists';
objHasOwnProperty(example, 'prop');   // true - 'prop' has been defined

example.prop = null;
objHasOwnProperty(example, 'prop');   // true - own property exists with value of null

example.prop = undefined;
objHasOwnProperty(example, 'prop');   // true - own property exists with value of undefined
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