javascript

Chapter 22: The Evolution of JavaScript
Here, the person object is used as the prototype of two new objects. Initially, anotherPerson and
yetAnotherPerson have only properties referenced from person (their prototype). You can overwrite
the name property so each has its own name property and is no longer using person.name , but all
instances share the same friends property, so changes made through one object affect all others.
By providing a second argument to Object.create() , you can also add new properties to the
created object. Consider the following:
var person = {
name: “Nicholas”,
friends: [“Shelby”, “Court”, “Van”]
};
var anotherPerson = Object.create(person, {
name: {
value: “Greg”
}
});
alert(anotherPerson.hasOwnProperty(“name”));
anotherPerson.friends.push(“Rob”);
//true
In this example, the anotherPerson object is created by using Object.create() and passing in a
second argument. The resulting object still has its own name property and doesn ’ t use the one on
the prototype. This property was created as its descriptor was specified in the second argument. The
Object.create() method is therefore ideal for prototypal inheritance of individual objects (as opposed
to objects based on custom constructors).
The second method for creating objects is Object.clone() . This method accepts a single argument,
which is the object to clone, and returns an object. The returned object is a clone of the original in that its
has the same prototype and the same instance properties. Here is an example:
var person = {
name: “Nicholas”,
age: 29
};
var employee = Object.create(person, {
job: {
value: “Software Engineer”
}
});
var employee2 = Object.clone(employee);
alert(employee.name); //”Nicholas”
alert(employee2.name); //”Nicholas”
alert(employee.hasOwnProperty(“job”)); //true
alert(employee2.hasOwnProperty(“job”)); //true
alert(employee.getPrototypeOf() === employee2.getProtoypeOf());
//true
This code creates a clone of the employee object and stores it in a variable named employee2 . This
new object has the same prototype, person , as the original employee object and also has an instance
property called job . Note that employee.job and employee2.job are not related to one another and
are both instance properties of their respective objects.
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