fsPromises.readFile(path[, options])

• path <string> | <Buffer> | <URL> | <FileHandle> 文件名或 FileHandle
• 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
• 返回: <Promise> 使用文件的内容履行。

异步地读取文件的全部内容。

如果未指定编码（使用 options.encoding），则数据作为 <Buffer> 对象返回。 否则，数据将为字符串。

如果 options 是字符串，则它指定编码。

当 path 是目录时，fsPromises.readFile() 的行为是特定于平台的。 在 macOS、Linux 和 Windows 上，promise 将使用错误拒绝。 在 FreeBSD 上，将返回目录内容的表示。

读取位于运行代码同一目录下的 package.json 文件的示例：

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();

可以使用 <AbortSignal> 中止正在进行的 readFile。 如果请求中止，则返回的 promise 将使用 AbortError 拒绝：

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

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

  // 在 promise 达成之前中止请求。
  controller.abort();

  await promise;
} catch (err) {
  // 当请求中止时 - err 是 AbortError
  console.error(err);
}

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。

任何指定的 <FileHandle> 必须支持读取。

• path <string> | <Buffer> | <URL> | <FileHandle> filename or FileHandle
• options <Object> | <string>
  • encoding <string> | <null> Default: null
  • flag <string> See support of file system flags. Default: 'r'.
  • signal <AbortSignal> allows aborting an in-progress readFile
• Returns: <Promise> Fulfills with the contents of the file.

Asynchronously reads the entire contents of a file.

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

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

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.

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();

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);
}

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

Any specified <FileHandle> has to support reading.