使用 writeFile 或 writeFileSync 写入文件

var fs = require('fs');

// Save the string "Hello world!" in a file called "hello.txt" in
// the directory "/tmp" using the default encoding (utf8).
// This operation will be completed in background and the callback
// will be called when it is either done or failed.
fs.writeFile('/tmp/hello.txt', 'Hello world!', function(err) {
  // If an error occurred, show it and return
  if(err) return console.error(err);
  // Successfully wrote to the file!
});

// Save binary data to a file called "binary.txt" in the current
// directory. Again, the operation will be completed in background.
var buffer = new Buffer([ 0x48, 0x65, 0x6c, 0x6c, 0x6f ]);
fs.writeFile('binary.txt', buffer, function(err) {
  // If an error occurred, show it and return
  if(err) return console.error(err);
  // Successfully wrote binary contents to the file!
});

fs.writeFileSync 的行为与 fs.writeFile 类似，但不会在同步完成时进行回调，因此会阻塞主线程。大多数 node.js 开发人员更喜欢异步变体，它们几乎不会导致程序执行延迟。

注意：阻塞主线程是 node.js 中的错误做法。只有在调试时或没有其他选项可用时才应使用同步功能。

// Write a string to another file and set the file mode to 0755
try {
  fs.writeFileSync('sync.txt', 'anni', { mode: 0o755 });
} catch(err) {
  // An error occurred
  console.error(err);
}