使用 Node.js 从文件夹中读取所有文件

Question

For reading a file from a folder it's quite straightforward. The file was in.md format and transformed to html format before sending it with POST:

const express = require('express');
const bodyParser = require('body-parser');
const showdown = require('showdown');
const app = express();
const port = process.env.PORT || 5000;
app.use(bodyParser.json());
app.use(bodyParser.urlencoded({ extended: true }));

converter = new showdown.Converter();

app.post('/api/world', (req, res) => {
  fs = require('fs');
  fs.readFile(
    __dirname + '/posts/my-file.md',
    'utf8',
    function (err, data) {
      if (err) {
        return console.log(err);
      }
      text = data;
      html = converter.makeHtml(text);
      res.send(html);
    }
  );
});

app.listen(port, () => console.log(`Listening on port ${port}`));

Now, what happens when there are more files in that folder? For getting those files titles I did it like:

fs = require('fs');
fs.readdir(__dirname + '/posts', (err, files) => {
  if (err) console.log(err);
  else {
    console.log('\nCurrent directory filenames:');
    files.forEach((file) => {
      console.log(file);
    });
  }
});

The above code logs the titles of the files in that folder.

The problem appears when I want to read those files and send them as I did with the first single file at the beginning. This is how I've tried:

app.post('/api/world', (req, res) => {
  fs = require('fs');
  fs.readdir(__dirname + '/posts', (err, files) => {
    if (err) console.log(err);
    else {
      console.log('\nCurrent directory filenames:');
      files.forEach((file) => {
        // console.log(file);
        fs.readFile(__dirname + '/posts/' + file, 'utf8', function (err, data) {
          console.log(file);
          if (err) {
            return console.log(err);
          }
          text = data;
          html = converter.makeHtml(text);
          res.send(html);
        });
      });
    }
  });
});

It throws this error:

        res.send(html);
        ^

ReferenceError: res is not defined

I don't get it, res was defined at the top of the POST request. What's wrong with it and how can it be changed to work?

Answer 1

You only get ONE res.send() per request so if you're using res.send() you will have to accumulate the content and then send all the content at once.

And, since you have multiple asynchronous operations all in flight at once, you will also have to keep track of when they are all done. This would be easiest using promises with async/await .

Assuming you want to just concatenate all the HTML you produce, you can do something like this:

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

app.post('/api/world', async (req, res) => {
    try {
        let html = "";
        const basePath = path.join(__dirname, 'posts');
        const files = await fsp.readdir(basePath);
        for (let f of files) {
            const fileData = await fsp.readFile(path.join(basePath, f));
            html += converter.makeHtml(fileData);
        }
        res.send(html);
    } catch(e) {
        // log error and send error response
        console.log(e);
        res.sendStatus(500);
    }
});