Question: ```
alert(typeof QuizParser.Parser.otherdata['response_set']['answers']["slide_" + _index]['trt']);​

```

Why? Shouldn't this simply alert the string `undefined`? If this is wrong, how should I check to see if that variable is defined or not?

Answer: 
The error has nothing to do with `typeof`, it's because you're attempting to access a property of an undefined variable: `QuizParser.Parser`
When you use `typeof`, it will return `"undefined"` for undefined variables, but in your case you are actually doing other things before calling `typeof`. `QuizParser.Parser.otherdata` must be defined in order for `typeof` to not cause an error. For example, if `x` is not defined, `typeof(x)` is okay but `typeof(x.something)` will cause an error since you are trying to access `x` which is not defined (in order to access something)