fsPromises.readFile(path[, options])

• path <string> | <Buffer> | <URL> | <FileHandle> 文件名或 FileHandle
• options <Object> | <string>
  • encoding <string> | <null> 默认: null
  • flag <string> 参见 对文件系统 flags 的支持。默认值：'r'。
  • signal <AbortSignal> 允许中止正在进行的 readFile 操作
  • buffer <Buffer> | <TypedArray> | <DataView> | <Function> 一个用于读取的缓冲区，或者一个以文件大小为参数返回缓冲区的函数。
• 返回：<Promise> 用文件的内容填充。

异步地读取文件的全部内容。

🌐 Asynchronously reads the entire contents of a file.

如果未指定编码（使用 options.encoding），数据将作为 <Buffer> 对象返回。否则，数据将是一个字符串。

🌐 If no encoding is specified (using options.encoding), the data is returned as a <Buffer> object. Otherwise, the data will be a string.

如果 options 是字符串，那么它指定了编码。

🌐 If options is a string, then it specifies the encoding.

如果提供了 buffer 且没有指定编码，返回的 <Buffer> 将是对提供的缓冲区的一个视图，只包含读取的字节。如果提供的缓冲区太小，无法容纳整个文件，Promise 将会被拒绝。

🌐 If buffer is provided and no encoding is specified, the returned <Buffer> is a view over the supplied buffer containing only the bytes read. If the supplied buffer is too small to contain the entire file, the promise will be rejected.

当 path 是一个目录时，fsPromises.readFile() 的行为取决于平台。在 macOS、Linux 和 Windows 上，Promise 会被拒绝并返回一个错误。在 FreeBSD 上，将返回该目录内容的表示。

🌐 When the path is a directory, the behavior of fsPromises.readFile() is platform-specific. On macOS, Linux, and Windows, the promise will be rejected with an error. On FreeBSD, a representation of the directory's contents will be returned.

在运行代码的同一目录中读取 package.json 文件的示例：

🌐 An example of reading a package.json file located in the same directory of the running code:

import { readFile } from 'node:fs/promises';
try {
  const filePath = new URL('./package.json', import.meta.url);
  const contents = await readFile(filePath, { encoding: 'utf8' });
  console.log(contents);
} catch (err) {
  console.error(err.message);
}const { readFile } = require('node:fs/promises');
const { resolve } = require('node:path');
async function logFile() {
  try {
    const filePath = resolve('./package.json');
    const contents = await readFile(filePath, { encoding: 'utf8' });
    console.log(contents);
  } catch (err) {
    console.error(err.message);
  }
}
logFile();拷贝

可以使用 <AbortSignal> 中止正在进行的 readFile。如果请求被中止，返回的 Promise 将以 AbortError 拒绝：

🌐 It is possible to abort an ongoing readFile using an <AbortSignal>. If a request is aborted the promise returned is rejected with an AbortError:

import { readFile } from 'node:fs/promises';

try {
  const controller = new AbortController();
  const { signal } = controller;
  const promise = readFile(fileName, { signal });

  // Abort the request before the promise settles.
  controller.abort();

  await promise;
} catch (err) {
  // When a request is aborted - err is an AbortError
  console.error(err);
} 拷贝

中止正在进行的请求并不会中止单个操作系统请求，而是中止内部缓冲 fs.readFile 所执行的操作。

🌐 Aborting an ongoing request does not abort individual operating system requests but rather the internal buffering fs.readFile performs.

任何指定的 <FileHandle> 都必须支持读取。

🌐 Any specified <FileHandle> has to support reading.

使用预分配缓冲区和 buffer 选项的示例：

🌐 An example using the buffer option with a pre-allocated buffer:

import { Buffer } from 'node:buffer';
import { readFile } from 'node:fs/promises';

const buf = Buffer.alloc(16384);
const contents = await readFile('/path/to/file', { buffer: buf });
console.log(contents); // A view over `buf` containing only the bytes read 拷贝

使用 buffer 选项和返回缓冲区的函数的示例：

🌐 An example using the buffer option with a function returning a buffer:

import { Buffer } from 'node:buffer';
import { readFile } from 'node:fs/promises';

const contents = await readFile('/path/to/file', {
  buffer: (size) => Buffer.alloc(size),
});
console.log(contents); 拷贝