Refresh function every time there is a change in the cloud-CodePudding

I have a function that works, the problem is that I want it to work again every time there is a change in the variable "QR" (variable QR receives updates from the cloud) and it stays the same. The function that should be enabled "QRCode.toDataURL".

client.on('qr', qr => {
qrcode.generate(qr, {small: true});
let qrcode1 = qr;
console.log(qr)
app.get('/', function (req, res) {

let opts = {
    errorCorrectionLevel: 'H',
    type: 'image/jpeg',
    quality: 0.3,
    margin: 1,
    color: {
      dark:"#010599FF",
      light:"#40FF60"
    }
  }
  
  QRCode.toDataURL(qr, opts, function (err, url) {
    if (err) throw err
    res.send(`<img src='${src = url}'>`)
  })

  })

});

CodePudding user response：

You need to save it in a global variable, it should be an array or object since we need reference.

const qrCodes = [] //

update that entry of index 0 every time you get new qr code.

client.on('qr', (qr) => {
  qrCodes[0] = qr
})

consume the same every time request comes in

app.get('/', function (req, res) {
  let opts = {
    errorCorrectionLevel: 'H',
    type: 'image/jpeg',
    quality: 0.3,
    margin: 1,
    color: {
      dark: '#010599FF',
      light: '#40FF60',
    },
  }

  const qrCode = qrCodes[0]
  if (!qrCode) return res.send('')

  QRCode.toDataURL(qr, opts, function (err, url) {
    if (err) throw err
    res.send(`<img src='${(src = url)}'>`)
  })
})

It might be better to convert qrcode into DataURL string on the fly and send that string directly to user instead of generating it over 'n over but I leave it to you.