fs.copyFile(src, dest[, mode], callback)

• src <string> | <Buffer> | <URL> 要复制的源文件名
• dest <string> | <Buffer> | <URL> 复制操作的目标文件名
• mode <integer> 复制操作的修饰符。 默认值: 0。
• callback <Function>

异步地将 src 复制到 dest。 默认情况下，如果 dest 已经存在，则会被覆盖。 除了可能的异常之外，没有给回调函数提供任何参数。 Node.js 不保证复制操作的原子性。 如果在打开目标文件进行写入后发生错误，Node.js 将尝试删除目标文件。

mode 是可选的整数，用于指定复制操作的行为。 可以创建由两个或多个值的按位或组成的掩码（例如 fs.constants.COPYFILE_EXCL | fs.constants.COPYFILE_FICLONE）。

• fs.constants.COPYFILE_EXCL: 如果 dest 已经存在，则复制操作将失败。
• fs.constants.COPYFILE_FICLONE: 复制操作将尝试创建写时复制引用链接。 如果平台不支持写时复制，则使用后备复制机制。
• fs.constants.COPYFILE_FICLONE_FORCE: 复制操作将尝试创建写时复制引用链接。 如果平台不支持写时复制，则该操作将失败。

import { copyFile, constants } from 'fs';

function callback(err) {
  if (err) throw err;
  console.log('source.txt was copied to destination.txt');
}

// 默认情况下将创建或覆盖 destination.txt。
copyFile('source.txt', 'destination.txt', callback);

// 通过使用 COPYFILE_EXCL，如果 destination.txt 存在，则该操作将失败。
copyFile('source.txt', 'destination.txt', constants.COPYFILE_EXCL, callback);

• src <string> | <Buffer> | <URL> source filename to copy
• dest <string> | <Buffer> | <URL> destination filename of the copy operation
• mode <integer> modifiers for copy operation. Default: 0.
• callback <Function>

Asynchronously copies src to dest. By default, dest is overwritten if it already exists. No arguments other than a possible exception are given to the callback function. Node.js makes no guarantees about the atomicity of the copy operation. If an error occurs after the destination file has been opened for writing, Node.js will attempt to remove the destination.

mode is an optional integer that specifies the behavior of the copy operation. It is possible to create a mask consisting of the bitwise OR of two or more values (e.g. fs.constants.COPYFILE_EXCL | fs.constants.COPYFILE_FICLONE).

• fs.constants.COPYFILE_EXCL: The copy operation will fail if dest already exists.
• fs.constants.COPYFILE_FICLONE: The copy operation will attempt to create a copy-on-write reflink. If the platform does not support copy-on-write, then a fallback copy mechanism is used.
• fs.constants.COPYFILE_FICLONE_FORCE: The copy operation will attempt to create a copy-on-write reflink. If the platform does not support copy-on-write, then the operation will fail.

import { copyFile, constants } from 'fs';

function callback(err) {
  if (err) throw err;
  console.log('source.txt was copied to destination.txt');
}

// destination.txt will be created or overwritten by default.
copyFile('source.txt', 'destination.txt', callback);

// By using COPYFILE_EXCL, the operation will fail if destination.txt exists.
copyFile('source.txt', 'destination.txt', constants.COPYFILE_EXCL, callback);