Node.js · Chapter 41 of 43
Handling File Uploads
File uploads require parsing multipart/form-data request bodies, which is more complex than simple JSON. The `multer` middleware handles this parsing for Express apps.
Uploaded files can be stored on disk, in memory, or forwarded to cloud storage like S3.
Setting up multer
Configure `multer` with a storage destination, then use it as middleware on routes that accept file uploads.
Accessing uploaded files
Multer attaches uploaded file info to `req.file` (single upload) or `req.files` (multiple uploads).
Example 1 (javascript)
const multer = require('multer');
const upload = multer({ dest: 'uploads/' });
app.post('/upload', upload.single('avatar'), (req, res) => {
res.json({ filename: req.file.filename });
});Output
{"filename":"a1b2c3.png"}multer.single() parses one uploaded file field named 'avatar' and saves it to disk.
Example 2 (javascript)
app.post('/gallery', upload.array('photos', 5), (req, res) => {
res.json({ count: req.files.length });
});Output
{"count":3}upload.array() handles multiple files under the same field name, up to a max count.
Key points
- File uploads use multipart/form-data, requiring special parsing.
- multer is the standard Express middleware for handling uploads.
- req.file/req.files hold uploaded file metadata.
- Files can be stored on disk, in memory, or forwarded to cloud storage.
💡 Note: Always validate file type and size to avoid storage abuse or malicious uploads.