使用 writeFile 或 writeFileSync 寫入檔案

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 的行為與 fs.writeFile 類似，但不會在同步完成時進行回撥，因此會阻塞主執行緒。大多數 node.js 開發人員更喜歡非同步變體，它們幾乎不會導致程式執行延遲。

注意：阻塞主執行緒是 node.js 中的錯誤做法。只有在除錯時或沒有其他選項可用時才應使用同步功能。

// 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);
}