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Last updated on 2/21/22

Accept Incoming Files With Multer

In this final part of the course, you will learn how to implement file uploads to allow users to upload images of items they want to sell. To do this, you will use  multer  , a package that allows you to handle incoming files in HTTP requests. So let's start by installing  multer  and building a piece of middleware to handle those incoming files.

Set Up File Handling Middleware

First you need to install  multer  to your project:

npm install multer

Now you can create a new piece of middleware in your  middleware  folder called  multer-config.js :

const multer = require('multer');

const MIME_TYPES = {
  'image/jpg': 'jpg',
  'image/jpeg': 'jpg',
  'image/png': 'png'

const storage = multer.diskStorage({
  destination: (req, file, callback) => {
    callback(null, 'images');
  filename: (req, file, callback) => {
    const name = file.originalname.split(' ').join('_');
    const extension = MIME_TYPES[file.mimetype];
    callback(null, name + Date.now() + '.' + extension);

module.exports = multer({storage: storage}).single('image');

In this middleware:

  • Create a  storage  constant — to be passed to  multer  as configuration, which contains the logic necessary for telling  multer  where to save incoming files.

    • The  destination  function tells  multer  to save files in the  images  folder.

    • The  filename  function tells  multer  to use the original name, replacing any spaces with underscores and adding a  Date.now()  timestamp, as the file name; it then uses the MIME type map constant to resolve the appropriate file extension.

  • You then export the fully configured  multer , passing it your  storage  constant, and telling it that you will be handling uploads of single image files.

Let's Recap!

  • multer  is a file-handling package.

  • Multer's  diskStorage()  sets up the destination path and filename for incoming files.

  • Multer's  single()  method creates middleware which captures single files of the type passed as an argument and uses the set storage method to save it to the server's filesystem.

Before you can apply your middleware to your stuff routes, you need to modify them slightly, as the structure of the incoming data is not quite the same when there are files and JSON data. This is what we will do in the next chapter! 

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