Checking if a variable exists in javascript

Question

I know there are two methods to determine if a variable exists and not null(false, empty) in javascript:

1) if ( typeof variableName !== \'undefined\' && v

Answer 1

I'm writing an answer only because I do not have enough reputations to comment the accepted answer from apsillers. I agree with his answer, but

If you really want to test if a variable is undeclared, you'll need to catch the ReferenceError ...

is not the only way. One can do just:

this.hasOwnProperty("bar")

to check if there is a variable bar declared in the current context. (I'm not sure, but calling the hasOwnProperty could also be more fast/effective than raising an exception) This works only for the current context (not for the whole current scope).