Now we come to a tricky area. In JavaScript functions are objects - yes they can have properties and methods. They can therefore have toString and valueOf methods. What this means is that a function can return three different values depending on how it is used.
This also raises the issue of why bother using a function if general objects can return a value?
The reason is fairly obvious but deserves some thought.
Functions Versus Objects
You do have a choice of associating a value with an object as in:
myObject+1;
You also can define a function that does the same thing:
myFunction()+1;
The difference is that the function has a natural way to accept arguments. For example, you can write:
myFunction(10)+1;
but without defining it to be a function you can't write:
myObject(10)+1;
In other words, objects can simply represent a value or a state. That value or state can be manipulated by the methods that the object provides but it cannot be modified while it is being used in an expression.
A function, on the other hand, represents a relationship between input data and the result.
Notice also that, while a function is an object, not all objects are functions and in this sense a function is a "bigger" object.
When should you consider using a value associated with an object?
Some might reply "never" as it isn't a common pattern and could be confusing.
However, if an object represents data or something with state then it is a good approach.
Consider the JavaScript date object:
var d=Date.now(); alert(d);
The toString function returns the number of milliseconds since the date epoch. A Date object is an ideal example of when to use an object as a value.
Javascript, being an interpreted language, can modify its own code as it runs. Self-modifying code can be dangerous but you should know about it and how it works. If you would like to experiment, [ ... ]
