Upload File with Unique File Name Specified by Client

We can provide unique file name by Client and specify this name to Multer.

Version

Node 16.16.0
Express 4.17.1
Alpine 3.10.3

Alpine

unique000

Upload single file by Alpine and Express.

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <script src="https://unpkg.com/alpinejs" defer></script>
    <title>Upload</title>
  </head>
  <body x-data="fileUpload">
    <input x-ref="upload" type="file" />
    <button @click="onClick">Upload</button>
    <div x-text="resMsg"></div>
  </body>
  <script>
    let fileUpload = {
      resMsg: '',
      async onClick() {
        let newFileName = Date.now() + '-' + Math.round(Math.random() * 1E9)

        let formData = new FormData()
        formData.append('newFileName', newFileName)
        formData.append('file', this.$refs.upload.files[0])

        try {
          let res = await fetch(`http://localhost:8080/upload`, {
            method: 'POST',
            body: formData,
          })

          let data = await res.json()
          this.resMsg = data.message
        } catch (e) {
          console.error(e)
        }
      },
    }
  </script>
</html>

Line 8

<body x-data="fileUpload">
  <input x-ref="upload" type="file" />
  <button @click="onClick">Upload</button>
  <div x-text="resMsg"></div>
</body>

x-data：with fileUpload Object to control the component
x-ref：to set the name for the DOM element
@click：upload the file to the server
x-text：display the result message

Line 17

let newFileName = Date.now() + '-' + Math.round(Math.random() * 1E9)

Determine a random file name

Line 19

let formData = new FormData()
formData.append('newFileName', newFileName)
formData.append('file', this.$refs.upload.files[0])

fetch() accepts FormData as argument for body
Append newFileName key for other POST data
Append file key for uploaded file

Line 23

try {
  let res = await fetch(`http://localhost:8080/upload`, {
    method: 'POST',
    body: formData,
  })

  let data = await res.json()
  this.resMsg = data.message
} catch (e) {
  console.error(e)
}

Use fetch() API with method POST and body formData
response.json()：fetch() returns Promise with Response Object, use json() to convert Response Object to JSON Object

Express

import express, { json } from 'express'
import cors from 'cors'
import multer, { diskStorage } from 'multer'

let app = express()
app.use(cors())
app.use(json())

let storage = diskStorage({
  destination(req, file, cb) {
    cb(null, 'uploads')
  },
  filename(req, file, cb) {
    let { body: { newFileName }} = req
    cb(null, newFileName)
  },
})

let opts = multer({ storage }).single('file')

app.post('/upload', opts, (req, res) => {
  res.json({ message: 'Successfully uploaded files' })
})

app.listen(8080, () => {
  console.log('Node listen on port: 8080')
})

Line 1

import express, { json } from 'express'
import cors from 'cors'
import multer, { diskStorage } from 'multer'

Import express、cors and multer

Line 5

let app = express()

Create app Object for Express

Line 6

app.use(cors())

Create cors middleware by cors()
Use cors middleware by Express

Line 7

app.use(json())

Create json middleware by json(). This is a built-in middleware by Express
Use json middleware by Express

Line 9

let storage = diskStorage({
  destination(req, file, cb) {
    cb(null, 'uploads')
  },
  filename(req, file, cb) {
    let { body: { newFileName }} = req
    cb(null, newFileName)
  },
})

Use diskStorage() to create storage Object for Multer options
destination：determine within which folder the uploaded files should be stored
filename：determine what the file should be named inside the folder, get newFileNmae from req and cb() to set new file name

Line 19

let opts = multer({ storage }).single('file')

Create opts Object for Multer
dest：set folder to place files
single：upload single file by Multer, the argument for single() must depend on the name for the input specified in formData in Alpine

Line 21

app.post('/upload', opts, (req, res) => {
  res.json({ message: 'Successfully uploaded files' })
})

Create /upload POST with Multer options
Use Object Destructuring to destructure req Object to get other POST data
Return JSON Object with successful message

Line 25

app.listen(8080, () => {
  console.log('Node listen on port: 8080')
})

Express listens on port 8080

Conclusion

We can get POST data in filename() of storage Object to set unique file name specified by client