forEach方法中的function回调支持3个参数：
value：遍历的数组内容；index：对应的数组索引，array：数组本身。

[].forEach(function(value, index, array) {
  // ...
});

例：

data数据

{"posts":[{"userID":1,"userName":"linger","password":"linger","gender":0,"identity":1},{"userID":2,"userName":"andre","password":"andre","gender":0,"identity":2},{"userID":3,"userName":"admin","password":"admin","gender":0,"identity":3},{"userID":4,"userName":"shumei","password":"shumei","gender":1,"identity":2}]}

js语句

data.posts.forEach(function (value, , array) {
                console.log(value);
                console.log(index);
                console.log(array);
            })

console输出