docs: function zadd(members) {
    var i
      , c = 0
      , score
      , member;
    for(i = 0;i < members.length;i+=2) {
      score = members[i];
      if(INFINITY[score] !== undefined) {
        score = INFINITY[score];
      }
      member = members[i + 1];
      if(this.zrank(member) === null) {
        c++;
      }
      // this will add or update the score
      this.setKey(member, score);
    }
    return c;
  }