spec/lib/jspec.js
function(callback, a, b) {
       return callback.length == 1 ? callback(b) : callback(a, b)
     }
function(callback, a, b) {
       return callback.length == 1 ? callback(b) : callback(a, b)
     }
function ( callback , a , b ) { return callback . length == 1 ? callback ( b ) : callback ( a , b ) }
Call an iterator callback with arguments a, or b
depending on the arity of the callback.

@param  {function} callback
@param  {mixed} a
@param  {mixed} b
@return {mixed}
@api private
Call an iterator callback with arguments a or b depending on the arity of the callback .