path <string> | <Buffer> | <URL>
path
len <integer> 默认值：0
len
0
¥len <integer> Default: 0
返回：<Promise> 成功时将使用 undefined 履行。
undefined
¥Returns: <Promise> Fulfills with undefined upon success.
将 path 上的内容截断（缩短或延长长度）到 len 个字节。
¥Truncates (shortens or extends the length) of the content at path to len bytes.