fs.readFile(path[, options], callback)
path
<string> | <Buffer> | <URL> | <integer> 文件名或文件描述符options
<Object> | <string>encoding
<string> | <null> 默认值:null
flag
<string> 请参阅对文件系统flags
的支持。 默认值:'r'
。signal
<AbortSignal> 允许中止正在进行的读取文件
callback
<Function>err
<Error> | <AggregateError>data
<string> | <Buffer>
异步地读取文件的全部内容。
import { readFile } from 'fs';
readFile('/etc/passwd', (err, data) => {
if (err) throw err;
console.log(data);
});
回调传入了两个参数 (err, data)
,其中 data
是文件的内容。
如果未指定编码,则返回原始缓冲区。
如果 options
是字符串,则它指定编码:
import { readFile } from 'fs';
readFile('/etc/passwd', 'utf8', callback);
当路径是目录时,fs.readFile()
和 fs.readFileSync()
的行为是特定于平台的。
在 macOS、Linux 和 Windows 上,将返回错误。
在 FreeBSD 上,将返回目录内容的表示。
import { readFile } from 'fs';
// macOS、Linux 和 Windows
readFile('<directory>', (err, data) => {
// => [Error: EISDIR: illegal operation on a directory, read <directory>]
});
// FreeBSD
readFile('<directory>', (err, data) => {
// => null, <data>
});
可以使用 AbortSignal
中止正在进行的请求。
如果请求被中止,回调将被使用 AbortError
调用:
import { readFile } from 'fs';
const controller = new AbortController();
const signal = controller.signal;
readFile(fileInfo[0].name, { signal }, (err, buf) => {
// ...
});
// 当想中止请求时
controller.abort();
fs.readFile()
函数缓冲整个文件。
为了最小化内存成本,在可能的情况下优先通过 fs.createReadStream()
进行流式传输。
中止正在进行的请求不会中止单个操作系统请求,而是中止内部缓冲的 fs.readFile
执行。
path
<string> | <Buffer> | <URL> | <integer> filename or file descriptoroptions
<Object> | <string>encoding
<string> | <null> Default:null
flag
<string> See support of file systemflags
. Default:'r'
.signal
<AbortSignal> allows aborting an in-progress readFile
callback
<Function>err
<Error> | <AggregateError>data
<string> | <Buffer>
Asynchronously reads the entire contents of a file.
import { readFile } from 'fs';
readFile('/etc/passwd', (err, data) => {
if (err) throw err;
console.log(data);
});
The callback is passed two arguments (err, data)
, where data
is the
contents of the file.
If no encoding is specified, then the raw buffer is returned.
If options
is a string, then it specifies the encoding:
import { readFile } from 'fs';
readFile('/etc/passwd', 'utf8', callback);
When the path is a directory, the behavior of fs.readFile()
and
fs.readFileSync()
is platform-specific. On macOS, Linux, and Windows, an
error will be returned. On FreeBSD, a representation of the directory's contents
will be returned.
import { readFile } from 'fs';
// macOS, Linux, and Windows
readFile('<directory>', (err, data) => {
// => [Error: EISDIR: illegal operation on a directory, read <directory>]
});
// FreeBSD
readFile('<directory>', (err, data) => {
// => null, <data>
});
It is possible to abort an ongoing request using an AbortSignal
. If a
request is aborted the callback is called with an AbortError
:
import { readFile } from 'fs';
const controller = new AbortController();
const signal = controller.signal;
readFile(fileInfo[0].name, { signal }, (err, buf) => {
// ...
});
// When you want to abort the request
controller.abort();
The fs.readFile()
function buffers the entire file. To minimize memory costs,
when possible prefer streaming via fs.createReadStream()
.
Aborting an ongoing request does not abort individual operating
system requests but rather the internal buffering fs.readFile
performs.