在 fs.writeFile([option]) 中,"options parameter" 通常如何工作?
In fs.writeFile([option]), how an "options parameter" generally work?
我正在阅读这篇关于 Node.js 文件系统 fs.writeFile(filename, data, [options], callback)
的文档。
所以我注意到我经常看到[选项],但从来没有用过它。有人可以给我举个例子吗?我所有的案例都没有使用这个选项。
这些是选项。
- 编码(字符串或NULL),默认值为'utf8'
- 模式(数字),默认值为 438(即八进制中的 0666)
- flag(字符串),默认值为'w'
我猜您对 options
参数在 javascript 中的一般工作方式感兴趣。
与相反,参数是stated in the docs:
- options Object
- encoding String | Null default = 'utf8'
- mode Number default = 438 (aka 0666 in Octal)
- flag String default = 'w'
一般来说,options
参数是一个对象,其属性就是你要修改的选项。因此,如果您想修改 fs.writeFile
上的两个选项,您可以将每个选项作为 属性 添加到 options
:
fs.writeFile(
"foo.txt",
"bar",
{
encoding: "base64",
flag: "a"
},
function(){ console.log("done!") }
)
如果您对这三个参数的用途感到困惑,the docs for fs.open
拥有您需要的一切。它包括 flag
的所有可能性以及 mode
的描述。 callback
在 writeFile
操作完成后被调用。
fs.writeFile(filename,data,{flag: "wx"},function(err){
if(err) throw err
console.log('Date written to file, ',filename)
})
正如您在上面的代码片段中看到的,第三个参数是options/flag。有optional和用来表示文件打开时的行为。
我已将 "wx" 作为选项传递,这表明文件将打开以进行写入,如果文件不存在则将被创建。但如果已经存在,它将失败。
默认情况下 "w" 作为选项传递。
要进一步阅读不同的选项,here
对于任何结束这里寻找标志参考的搜索,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.
我正在阅读这篇关于 Node.js 文件系统 fs.writeFile(filename, data, [options], callback)
的文档。
所以我注意到我经常看到[选项],但从来没有用过它。有人可以给我举个例子吗?我所有的案例都没有使用这个选项。
这些是选项。
- 编码(字符串或NULL),默认值为'utf8'
- 模式(数字),默认值为 438(即八进制中的 0666)
- flag(字符串),默认值为'w'
我猜您对 options
参数在 javascript 中的一般工作方式感兴趣。
与相反,参数是stated in the docs:
- options Object
- encoding String | Null default = 'utf8'
- mode Number default = 438 (aka 0666 in Octal)
- flag String default = 'w'
一般来说,options
参数是一个对象,其属性就是你要修改的选项。因此,如果您想修改 fs.writeFile
上的两个选项,您可以将每个选项作为 属性 添加到 options
:
fs.writeFile(
"foo.txt",
"bar",
{
encoding: "base64",
flag: "a"
},
function(){ console.log("done!") }
)
如果您对这三个参数的用途感到困惑,the docs for fs.open
拥有您需要的一切。它包括 flag
的所有可能性以及 mode
的描述。 callback
在 writeFile
操作完成后被调用。
fs.writeFile(filename,data,{flag: "wx"},function(err){
if(err) throw err
console.log('Date written to file, ',filename)
})
正如您在上面的代码片段中看到的,第三个参数是options/flag。有optional和用来表示文件打开时的行为。
我已将 "wx" 作为选项传递,这表明文件将打开以进行写入,如果文件不存在则将被创建。但如果已经存在,它将失败。
默认情况下 "w" 作为选项传递。
要进一步阅读不同的选项,here
对于任何结束这里寻找标志参考的搜索,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. |