Retrieve player stats. If you're only looking for the player's stats for a given week, you can optionally specify a week number. If no week number is specified, you'll get the full-season stats.
const YahooFantasy = require('yahoo-fantasy');
const yf = new YahooFantasy(
  Y!APPLICATION_KEY,
  Y!APPLICATION_SECRET,
  tokenCallbackFn, // optional
  redirectUri // optional
);
yf.setUserToken(
  Y!OAuthAccessToken
);
// promise based
try {
  const stats = await yf.player.stats(
    player_key,
    week // optional
  );
} catch (e) {
  // handle error
}
// callback based
yf.player.stats(
  player_key, 
  week, // optional
  callbackFn
);
{
  "player_key": "328.p.6619",
  "player_id": "6619",
  "name": {
    "full": "Albert Pujols",
    "first": "Albert",
    "last": "Pujols",
    "ascii_first": "Albert",
    "ascii_last": "Pujols"
  },
  "editorial_player_key": "mlb.p.6619",
  "editorial_team_key": "mlb.t.3",
  "editorial_team_full_name": "Los Angeles Angels",
  "editorial_team_abbr": "LAA",
  "uniform_number": "5",
  "display_position": "1B",
  "headshot": "http://l.yimg.com/iu/api/res/1.2/iium.CfIaaN.XDy7fB4Reg--/YXBwaWQ9eXZpZGVvO…g--/http://l.yimg.com/j/assets/i/us/sp/v/mlb/players_l/20130405/6619.1.jpg",
  "is_undroppable": "0",
  "position_type": "B",
  "eligible_positions": [
    "1B",
    "CI",
    "DH",
    "IF"
  ],
  "stats": {
    "coverage_type": "season",
    "coverage_value": "2014",
    "stats": [
      {
        "stat_id": "0",
        "value": "159"
      },
      {
        "stat_id": "1",
        "value": "159"
      },
      {
        "stat_id": "2",
        "value": "-"
      },
      {
        "stat_id": "6",
        "value": "633"
      },
      {
        "stat_id": "7",
        "value": "89"
      },
      {
        "stat_id": "8",
        "value": "172"
      },
      {
        "stat_id": "9",
        "value": "106"
      },
      {
        "stat_id": "10",
        "value": "37"
      },
      {
        "stat_id": "11",
        "value": "1"
      },
      {
        "stat_id": "12",
        "value": "28"
      },
      {
        "stat_id": "13",
        "value": "105"
      },
      {
        "stat_id": "14",
        "value": "0"
      },
      {
        "stat_id": "15",
        "value": "9"
      },
      {
        "stat_id": "16",
        "value": "5"
      },
      {
        "stat_id": "17",
        "value": "1"
      },
      {
        "stat_id": "18",
        "value": "48"
      },
      {
        "stat_id": "19",
        "value": "11"
      },
      {
        "stat_id": "20",
        "value": "5"
      },
      {
        "stat_id": "21",
        "value": "71"
      },
      {
        "stat_id": "22",
        "value": "28"
      },
      {
        "stat_id": "23",
        "value": "295"
      },
      {
        "stat_id": "51",
        "value": "879"
      },
      {
        "stat_id": "52",
        "value": "81"
      },
      {
        "stat_id": "53",
        "value": "3"
      },
      {
        "stat_id": "54",
        "value": ".997"
      },
      {
        "stat_id": "3",
        "value": ".272"
      },
      {
        "stat_id": "4",
        "value": ".324"
      },
      {
        "stat_id": "5",
        "value": ".466"
      },
      {
        "stat_id": "55",
        "value": ".790"
      },
      {
        "stat_id": "58",
        "value": "-"
      },
      {
        "stat_id": "59",
        "value": "-"
      },
      {
        "stat_id": "61",
        "value": "66"
      },
      {
        "stat_id": "62",
        "value": "4"
      },
      {
        "stat_id": "63",
        "value": ".833"
      },
      {
        "stat_id": "64",
        "value": "-"
      },
      {
        "stat_id": "65",
        "value": "695"
      },
      {
        "stat_id": "66",
        "value": "-"
      },
      {
        "stat_id": "86",
        "value": "0"
      },
      {
        "stat_id": "87",
        "value": "78"
      },
      {
        "stat_id": "88",
        "value": "0"
      }
    ]
  }
}