模仿jQuery的filter方法

$.fn.some = function(qualifier) {
  var self = this;
  return grep(this, false, function(self, index) {
    return qualifier.call(self, index);
  });
};
$.fn.every = function(qualifier) {
  var self = this;
  return grep(this, true, function(self, index) {
    return qualifier.call(self, index);
  });
};
?
function grep(ele, isEvery, callback) {
  for (var i = 0; i < ele.length; i++) {
    if (isEvery) {
      if (!callback(ele[i], i)) {
        return false;
      }
    } else {
      if (callback(ele[i], i)) {
        return true;
      }
    }
  }
  return isEvery;
}