Javascript Array filter(grade)

var school = [1, 2, 3, 4, 5, 6, 7, 8, 3, 35, 3, 5];

Array.prototype.filter = function(grade) {
  var result = [];
  this.forEach(function(item) {
    if (grade(item)) {
      result.push(item);//  w  w  w .  ja  v a2s .  com
    }
  });
  return result;
};

var a = school.filter(function(x) {
  return x > 3 && x < 8;
});

console.log(a);