is Array#map supported.js

      $jb._isFunction([].map) &&
      (function(){
        var n = 0
          , isFail = false
          , a = [1, 2, 3]
          , b = a.map(
            function(v, i, vs)
            {
              n |= 1 << i;
              
              if(vs != a)
                isFail = true;
            
              return 2*v;
            }
          )
        ;
        
        return !isFail && n == 7 && b.length == 3 && b[0] == 2 && b[1] == 4 && b[2] == 6; 
      })()