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.
The function object is the most important object in all of JavaScript and yet we tend to forget that it is an object. Understanding that JavaScript functions are objects is probably the most important [ ... ]
When you first meet it closure seems like the craziest of ideas. However once you realize that JavaScript functions are objects and what this implies then it seems like a natural consequence.
