javascript default value for argument

If you want to pass an argument with a default value in javascript this is how you do it.
http://stackoverflow.com/questions/894860/set-a-default-parameter-value-for-a-javascript-function

function foo(a, b)
 {
   a = typeof a !== 'undefined' ? a : 42;
   b = typeof b !== 'undefined' ? b : 'default_b';
   ...
 }