Question

I use this pattern to test for undefined and null values in ActionScript/Flex :

if(obj) {
    execute()
}

Unfortunately, a ReferenceError is always thrown when I use the pattern to test for child objects :

if(obj.child) {
    execute()
}

ReferenceError: Error #1069: Property child not found on obj and there is no default value.

Why does testing for child objects with if statements throw a ReferenceError?

Thanks!

Answer 1

You’re getting this error because the obj’s type does not have the child property in it. You need to do something like this:

if((obj) && (obj.hasOwnProperty('child') && (obj.child)){
 execute()
}

More info on the hasOwnProperty method in the Object class:
http://livedocs.adobe.com/flex/3/langref/Object.html#hasOwnProperty%28%29