Question

Hello fellow programmers, I have taken up learning JavaScript. This syntax is pure sorcery, can someone clarify:

function CleanPet(){
    alert("The pet is now clean!");
}

CleanPet.Description="Dirty Business";

The material I am reading explains that in JavaScript, functions are like any other object, but if I attach a property to a function, does this mean it is static, since I haven’t actually declared it?

Thanks for help,
I.N.

Answer 1

Object properties aren’t “declared” in the formal sense of using var like you do for variables. Given an existing object CleanPet, you can assign properties like CleanPet.Description (as in the question) which will create the Description property if it doesn’t already exist, or overwrite the property if it did already exist.

It is also “legal” to attempt to access object properties that you haven’t set yet, e.g., CleanPet.SomeOtherProperty – the resulting value will be undefined. (Not an error, though that assumes CleanPet actually is an object. If CleanPet is null or undefined then CleanPet.SomeOtherProperty would give an error.)

So regarding functions specifically, a function declaration:

 function CleanPet { /* some code */ }

…declares a single object that happens to be a function. Which means you can call it as a function CleanPet(), but it still gets “ordinary” object behaviour such as the ability to have properties assigned.

JavaScript functions are also object constructors if called with new:

var cleanPet1 = new CleanPet();

In that case JS creates a new object (instance) every time you call new CleanPet(), but the CleanPet.Description property is not accessible via cleanPet1.Description because it is a property of the constructor, not a property of the resulting new instance. So in that sense, yes, the property is “static”.