Question

Sample Code:

Dim myObject
Set myObject = JSON.parse(someJsonResponseFromTheServer)    

myFunction(myObject.someProperty)

The Problem:

When code similiar to this is ran in my application, it throws a 500 error from the server with a message similar to “Object Does not support property or method ‘someProperty’. What I would like to do to solve this problem is something like this:

Dim myObject
Set myObject = JSON.parse(someJsonResponseFromTheServer)    

If myObject.someProperty Then
    myFunction(myObject.someProperty)
End If

However, if I add the conditional, it throws the same error on the line with the conditional instead of the line with the method call.

My Question:

In ASP Classic, how do you detect if a property exists within an object without throwing an error?

Answer 1

One of the benefits of classic ASP is that it allows you to run both VBScript and JScript in the same page – thus you can use the power of both.

First, add this block of JScript code to your existing .asp file:

<script language="JScript" runat="server">
function CheckProperty(obj, propName) {
    return (typeof obj[propName] != "undefined");
}
</script>

And assuming VBScript is the default language in the page, you can call it from within your VBScript code like this:

Dim myObject
Set myObject = JSON.parse(someJsonResponseFromTheServer)    
If CheckProperty(myObject, "someProperty") Then
    myFunction(myObject.someProperty)
End If

Tested it with generic class object and it works fine – the JScript is compiled before the VBScript thus accessible to it.