回调与基于 promise 的操作的顺序

例如，以下内容容易出错，因为 fs.stat() 操作可能会在 fs.rename() 操作之前完成：

fs.rename('/tmp/hello', '/tmp/world', (err) => {
  if (err) throw err;
  console.log('renamed complete');
});
fs.stat('/tmp/world', (err, stats) => {
  if (err) throw err;
  console.log(`stats: ${JSON.stringify(stats)}`);
});

fs.rename('/tmp/hello', '/tmp/world', (err) => {
  if (err) throw err;
  fs.stat('/tmp/world', (err, stats) => {
    if (err) throw err;
    console.log(`stats: ${JSON.stringify(stats)}`);
  });
});

const fs = require('fs').promises;

(async function(from, to) {
  try {
    await fs.rename(from, to);
    const stats = await fs.stat(to);
    console.log(`stats: ${JSON.stringify(stats)}`);
  } catch (error) {
    console.error('there was an error:', error.message);
  }
})('/tmp/hello', '/tmp/world');

There is no guaranteed ordering when using either the callback or promise-based methods. For example, the following is prone to error because the fs.stat() operation might complete before the fs.rename() operation:

fs.rename('/tmp/hello', '/tmp/world', (err) => {
  if (err) throw err;
  console.log('renamed complete');
});
fs.stat('/tmp/world', (err, stats) => {
  if (err) throw err;
  console.log(`stats: ${JSON.stringify(stats)}`);
});

To correctly order the operations, move the fs.stat() call into the callback of the fs.rename() operation:

fs.rename('/tmp/hello', '/tmp/world', (err) => {
  if (err) throw err;
  fs.stat('/tmp/world', (err, stats) => {
    if (err) throw err;
    console.log(`stats: ${JSON.stringify(stats)}`);
  });
});

Or, use the promise-based API:

const fs = require('fs').promises;

(async function(from, to) {
  try {
    await fs.rename(from, to);
    const stats = await fs.stat(to);
    console.log(`stats: ${JSON.stringify(stats)}`);
  } catch (error) {
    console.error('there was an error:', error.message);
  }
})('/tmp/hello', '/tmp/world');