var DateProto = Date.prototype , INVALID_DATE = 'Invalid Date' , TO_STRING = 'toString' , $toString = DateProto[TO_STRING]; if(new Date(NaN) + '' != INVALID_DATE){ require('./$.redefine')(DateProto, TO_STRING, function toString(){ var value = +this; return value === value ? $toString.call(this) : INVALID_DATE; }); }