I have code that is wrapped in try/catch block.
I use typeof to find out if a variable is defined:

if (typeof (var) == 'string') { 

    //the string is defined

}

However, using this in a try/catch block, jumps to the catch part instead of doing what it is suppoed to do (do something with the string if its defined).

How can I check if a variable is defined without activating an exception?