QrcodeStream

Browser Support

This component fundamentally depends on the Stream API. Vue Native is not supported (see #206).

No	Yes	Yes	Yes¹	Yes²

1. Chrome requires HTTPS or localhost (see Troubleshooting for help)
2. Safari also requires HTTPS even on localhost (see #48). Support is limited for:
   • web apps added to home screen (PWA mode): at least iOS 13.4 (see #76)
   • iOS browsers other than Safari (Chrome for iOS, Firefox for iOS, ...): at least iOS 14.3 (see #29)
   • WkWebView component in native iOS apps: at least iOS 14.3 (see #29)

Events

decode

• Payload Type: String

Once a stream from the users camera is loaded, it's displayed and continuously scanned for QR codes. Results are indicated by the decode event.

<qrcode-stream @decode="onDecode"></qrcode-stream>

methods: {
  onDecode (decodedString) {
    // ...
  }
}

TIP

If you scan the same QR code multiple times in a row, decode is still only emitted once. When you hold a QR code in the camera, frames are actually decoded multiple times a second but you don't want to be flooded with decode events that often. That's why the last decoded QR code is always cached and only new results are propagated. However changing the value of camera resets this internal cache.

detect

• Payload Type: Promise<Object>

The detect event is basically a verbose version of decode. decode only gives you the string encoded by QR codes. detect on the other hand ...

• is always emitted before decode
• gives you the coordinates of the QR code in the camera frame
• does NOT silently fail in case of errors

<qrcode-stream @detect="onDetect"></qrcode-stream>

methods: {
  async onDetect (promise) {
    try {
      const {
        content,      // decoded String
        location      // QR code coordinates
      } = await promise

      // ...
    } catch (error) {
      // ...
    }
  }
}

init

• Payload Type: Promise<MediaTrackCapabilities>

It might take a while before the component is ready and the scanning process starts. The user has to be asked for camera access permission first and the camera stream has to be loaded.

If you want to show a loading indicator, you can listen for the init event. It's emitted as soon as the component is mounted. It carries a promise which resolves with the cameras MediaTrackCapabilities when everything is ready. The promise is rejected if initialization fails. This can have a couple of reasons.

WARNING

In Chrome you can't prompt users for permissions a second time. Once denied, users can only manually grant them. Make sure your users understand why you need access to their camera before you mount this component. Otherwise they might panic and deny and then get frustrated because they don't know how to change their decision.

<qrcode-stream @init="onInit"></qrcode-stream>

methods: {
  async onInit (promise) {
    // show loading indicator

    try {
      const { capabilities } = await promise

      // successfully initialized
    } catch (error) {
      if (error.name === 'NotAllowedError') {
        // user denied camera access permisson
      } else if (error.name === 'NotFoundError') {
        // no suitable camera device installed
      } else if (error.name === 'NotSupportedError') {
        // page is not served over HTTPS (or localhost)
      } else if (error.name === 'NotReadableError') {
        // maybe camera is already in use
      } else if (error.name === 'OverconstrainedError') {
        // did you requested the front camera although there is none?
      } else if (error.name === 'StreamApiNotSupportedError') {
        // browser seems to be lacking features
      }
    } finally {
      // hide loading indicator
    }
  }
}

Props

track

• Input Type: Function
• Default: undefined

You can visually highlight detected QR codes in real-time. A transparent canvas overlays the camera stream. When a QR code is detected, its location is painted to the canvas.

To enable this feature, pass a function to track that defines how this should look like. This function is called to produce each frame. It receives the location object as the first argument and a CanvasRenderingContext2D instance as the second argument.

For example check out the Custom Tracking Demo

Note that this scanning frequency has to be increased. So if you want to go easy on your target device you might not want to enable tracking.

WARNING

Avoid access to reactive properties in this function (like stuff in data, computed or your Vuex store). The function is called several times a second and might cause memory leaks. To be safe don't access this at all.

camera

• Input Type: String
• Default: auto
• Valid Inputs: auto, rear, front, off

With the camera prop you can control which camera to access on the users device.

• Use front or rear to force request the front or rear camera respectively.
• If you choose auto the rear camera is requested by default. But if a device like a laptop has only a front camera installed, auto will fallback to that.
• Use off to not request a camera at all or in other words: turn the camera off.

Every time the camera prop is modified, a new camera stream is requested so the init event is emitted again. That way you can catch errors. For example when the front camera is requested on a device that doesn't have one.

<qrcode-stream :camera="camera" @init="onCameraChange"></qrcode-stream>

data () {
  return {
    camera: 'auto'
  }
},

methods: {
  startFrontCamera () {
    this.camera = 'front'
  },

  onCameraChange (promise) {
    promise.catch(error => {
      const cameraMissingError = error.name === 'OverconstrainedError'
      const triedFrontCamera = this.camera === 'front'

      if (triedFrontCamera && cameraMissingError) {
        // no front camera on this device
      }
    })
  }
}

torch

• Input Type: Boolean
• Default: false

With the torch prop you can turn a devices flashlight on/off. This is not consistently supported by all devices and browsers. Support can even vary on the same device with the same browser. For example the rear camera often has a flashlight but the front camera doesn't. We can only tell if flashlight control is supported once the camera is loaded and the init event has been emitted. At the moment, torch silently fails on unsupported devices. But from the init events payload you can access the MediaTrackCapabilities object. This will tell you whether or not torch is supported.

Due to API limitations the camera stream must be reloaded when turning the torch on/off. That means the init event will be emitted again.

<qrcode-stream :torch="true" @init="onInit"></qrcode-stream>

methods: {
  async onInit (promise) {
    const { capabilities } = await promise

    const TORCH_IS_SUPPORTED = !!capabilities.torch
  }
}

worker removed in v3.0.0

old documentation

Slots

default

Any distributed content overlays the camera stream, wrapped in a position: absolute container.

<qrcode-stream>
  <b>stuff here overlays the camera stream</b>
</qrcode-stream>