在fs.writeFile([option])中,"options parameter"通常如何工作？

Question

我正在阅读有关Node.js文件系统的文档fs.writeFile(filename, data, [options], callback).所以我注意到我经常看到[选项],但从未用过任何东西.有人能举个例子吗？我所有的情况都没有使用这个选项.

Answer 1

我猜你对optionsjavascript中的参数通常如何工作很感兴趣.

与参数是什么相反,这些参数在文档中说明:

• 选项 对象
  • 编码 字符串 | Null default ='utf8'
  • mode Number默认= 438(八进制也称为0666)
  • flag String default ='w'

通常,options参数是一个对象,其属性是您要修改的选项.因此,如果您想要修改其中的两个选项fs.writeFile,则需要将每个选项作为属性添加到options:

fs.writeFile(
    "foo.txt",
    "bar",
    {
        encoding: "base64",
        flag: "a"
    },
    function(){ console.log("done!") }
)

如果你对这三个参数的用途感到困惑,那么文档就fs.open可以提供你需要的一切.它包括所有可能性flag和描述mode.在callback被调用一次的writeFile操作完成.

Answer 2

对于最终在这里寻找标志参考的任何人，这里是：

Flag Description r Open file for reading. An exception occurs if the file does not exist. r+ Open file for reading and writing. An exception occurs if the file does not exist. rs Open file for reading in synchronous mode. rs+ Open file for reading and writing, asking the OS to open it synchronously. See notes for 'rs' about using this with caution. w Open file for writing. The file is created (if it does not exist) or truncated (if it exists). wx Like 'w' but fails if the path exists. w+ Open file for reading and writing. The file is created (if it does not exist) or truncated (if it exists). wx+ Like 'w+' but fails if path exists. a Open file for appending. The file is created if it does not exist. ax Like 'a' but fails if the path exists. a+ Open file for reading and appending. The file is created if it does not exist. ax+ Like 'a+' but fails if the the path exists.