Javascript if typeof ='undefined' in try/catch space

Question

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?

Answer 1

'var' is not a valid variable name - it's a keyword.

Apart from that, what you have should be correct.

Answer 2

I would use a direct comparison without 'typeof':

var vvv= 2;
alert( vvv !== undefined );

Be careful, though, to know whether you want to check for truliness (not false, null, undefined, "" or 0), against null, undefined, false or a combination of these.

If you simply want to see that the value has a value, the code I placed above should do.

As a suggestion, I have found this book tremendous: JavaScript - the Good Parts

Answer 3

One point: typeof is an operator, not a function. You don't need parentheses around the operand.