回调的示例

回调的形式将完成回调函数作为其最后一个参数并且异步地调用该操作。 传给完成回调的参数取决于方法，但是第一个参数始终预留用于异常。 如果操作成功地完成，则第一个参数为 null 或 undefined。

const fs = require('fs');

fs.unlink('/tmp/hello', (err) => {
  if (err) throw err;
  console.log('successfully deleted /tmp/hello');
});

The callback form takes a completion callback function as its last argument and invokes the operation asynchronously. The arguments passed to the completion callback depend on the method, but the first argument is always reserved for an exception. If the operation is completed successfully, then the first argument is null or undefined.

const fs = require('fs');

fs.unlink('/tmp/hello', (err) => {
  if (err) throw err;
  console.log('successfully deleted /tmp/hello');
});