Mastering JavaScript

Chapter 2
Next, we define an object with a testObj variable with a property named
testObjFunc that receives a reference to testF()—don't fret if you are not really
aware of object creation yet. By doing this, we created a testObjMethod() method.
Now, when we invoke this method, we expect the function context to be displayed
when we display the value of this.
Invocation as a constructor
Constructor functions are declared just like any other functions and there's nothing
special about a function that's going to be used as a constructor. However, the way in
which they are invoked is very different.
To invoke the function as a constructor, we precede the function invocation with the
new keyword. When this happens, this is bound to the new object.
Before we discuss more, let's take a quick introduction to object orientation in
JavaScript. We will, of course, discuss the topic in great detail in the next chapter.
JavaScript is a prototypal inheritance language. This means that objects can inherit
properties directly from other objects. The language is class-free. Functions that
are designed to be called with the new prefix are called constructors. Usually, they
are named using PascalCase as opposed to CamelCase for easier distinction. In
the following example, notice that the greet function uses this to access the name
property. The this parameter is bound to Person:
var Person = function (name) {
this.name = name;
};
Person.prototype.greet = function () {
return this.name;
};
var albert = new Person('Albert Einstein');
console.log(albert.greet());
We will discuss this particular invocation method when we study objects in the next
chapter.
Invocation using apply() and call() methods
We said earlier that JavaScript functions are objects. Like other objects, they also
have certain methods. To invoke a function using its apply() method, we pass two
parameters to apply(): the object to be used as the function context and an array
of values to be used as the invocation arguments. The call() method is used in a
similar manner, except that the arguments are passed directly in the argument list
rather than as an array.
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