What is property in hasOwnProperty in JavaScript?

hasOwnProperty returns a boolean value indicating whether the object on which you are calling it has a property with the name of the argument. For example:

var x = {
    y: 10
};
console.log(x.hasOwnProperty("y")); //true
console.log(x.hasOwnProperty("z")); //false

However, it does not look at the prototype chain of the object.

It’s useful to use it when you enumerate the properties of an object with the for...in construct.

If you want to see the full details, the ES5 specification is, as always, a good place to look.