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Difference between this property descriptor and property assignment in ECMAScript 5?
var Person = {
    firstName: null, // the person’s first name
    lastName: null // the person’s last name
};

var Employee = Object.create(Person, {
    id: {
        value: null,
        enumerable: true,
        configurable: true,
        writable: true
    }
});

var Employee = Object.create(Person);
Employee.id = null;

// Or using jQuery.extend
$.extend(Employee, {
    id : null
});

obj.prop = val;

Object.defineProperty( obj, 'prop', {
    value: val
});