注意：生产代码可以处理对数组内不存在的属性的请求。

Note: Production code should handle requests for attributes that do not exist in the array.

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它接受单个参数：一个函数，并将此函数应用于数组内的每个元素。

It takes a single parameter, a function, and applies the function to each element in the array.

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current参数的初始值是数组内的第一个元素。

The current parameter starts off as the first element in the array.

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