vue-qrcode-reader

A Vue.js 2 component, accessing the device camera and allowing users to read QR codes, within the browser.

• read camera stream and/or drag-and-dropped images
• customizable visual tracking of QR codes
• responsive and layout agnostic

Demos

Browser support

No	Yes	Yes	Yes	11+

• Chrome requires HTTPS or localhost (see #38 for help)
• Safari also requires HTTPS even on localhost (see #48)
• on iOS it only works with Safari. Chrome or Firefox for iOS are not supported (see #29)
• more details on Caniuse

API

Prop	Valid Types	Default
:track	Boolean, Function	true
:paused	Boolean	false
:camera	Boolean, Object	see Usage

Event	Payload Type
@decode	String
@detect	Promise<Object>
@init	Promise<void>

Usage

decode event

Once a stream from the users camera is loaded, it is displayed and continuously scanned for QR codes. Results are indicated by the decode event. This also accounts for decoded images drag-and-dropped in the area the component occupies.

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

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

You might notice that when 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, you can clear this internal cache by setting the paused prop to true.

detect event

The detect event is quite similar to decode but it provides more details. decode only gives you the string encoded by QR codes. detect additionally

• tells you where results came from (i.e. a camera stream, a drag-and-dropped file or url)
• gives you the unprocessed raw image data
• the coordinates of the QR code in the image/camera frame

In case of errors decode also silently fails. For example when a non-image file is drag-and-dropped.

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

methods: {
  async onDetect (promise) {
    try {
      const {
        source,       // 'file', 'url' or 'stream'
        imageData,    // raw image data of image/frame
        content,      // decoded String
        location      // QR code coordinates
      } = await promise

      // ...
    } catch (error) {
      if (error.name === 'DropImageFetchError') {
        // drag-and-dropped URL (probably just an <img> element) from different
        // domain without CORS header caused same-origin-policy violation
      } else if (error.name === 'DropImageDecodeError') {
        // drag-and-dropped file is not of type image and can't be decoded
      } else {
        // idk, open an issue ¯\_(ツ)_/¯
      }
    }
  }
}

init event

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 and carries a promise which resolves when everything is ready. The promise is rejected if initialization fails. This can have a couple of reasons.

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

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

    try {
      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') {
        // passed constraints don't match any camera.
        // Did you requested the front camera although there is none?
      } else {
        // browser might be lacking features (WebRTC, ...)
      }
    } finally {
      // hide loading indicator
    }
  }
}

track prop

By default detected QR codes are visually highlighted. A transparent canvas overlays the camera stream. When a QR code is detected, its location is painted to the canvas. You can enable/disable this feature by passing true/false via the track prop. If tracking is disabled the camera stream is scanned much less frequently. So if you encounter performance problems on your target device, this might help.

You can also pass a function with track to customize the way the location is painted. 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.

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. If you want to be safe don't access this at all.

Say you want to paint in a different color that better fits your overall page theme.

<qrcode-reader :track="repaintLocation"></qrcode-reader>

methods: {
  repaintLocation (location, ctx) {
    const {
      topLeftCorner,
      topRightCorner,
      bottomLeftCorner,
      bottomRightCorner,
      // topLeftFinderPattern,
      // topRightFinderPattern,
      // bottomLeftFinderPattern
    } = location

    ctx.strokeStyle = 'blue' // instead of red

    ctx.beginPath()
    ctx.moveTo(topLeftCorner.x, topLeftCorner.y)
    ctx.lineTo(bottomLeftCorner.x, bottomLeftCorner.y)
    ctx.lineTo(bottomRightCorner.x, bottomRightCorner.y)
    ctx.lineTo(topRightCorner.x, topRightCorner.y)
    ctx.lineTo(topLeftCorner.x, topLeftCorner.y)
    ctx.closePath()

    ctx.stroke()
  }
}

default slot

Distributed content will overlay the camera stream, wrapped in a position: absolute container.

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

paused prop

With the paused prop you can prevent further decode propagation. Functions passed via track are also stopped being called. Useful for example if you want to validate results one at a time.

When the component is paused the camera stream freezes but is actually still running in the background. The browser will tell you that the camera is still in use. If you want to kill the stream completely you can pass false to the camera prop.

<qrcode-reader @decode="onDecode" :paused="paused"></qrcode-reader>

data () {
  return {
    paused: false
  }
},

methods: {
  onDecode (content) {
    this.paused = true
    // ...
  }
}

camera prop

With the camera prop you can filter the set of cameras installed on a client device. For example, if you want to access the front camera instead of the rear camera, pass this:

<qrcode-reader :camera="{ facingMode: 'user' }"></qrcode-reader>

This component uses getUserMedia to request camera streams. This method accepts a constraints object. By default this component passes this:

{
  audio: false, // don't request microphone access
  video: {
    facingMode: { ideal: 'environment' }, // use rear camera if available
    width: { min: 360, ideal: 680, max: 1920 }, // constrain video width resolution
    height: { min: 240, ideal: 480, max: 1080 }, // constrain video height resolution
  }
}

This video part in this object is essentially what you can change using the camera prop. Note that you only have to pass properties you want to override. All the other default properties on the first depth level are preserved. Here are a few examples:

camera="{ facingMode: 'user' }": the facingMode property is passed and is the only property that changes. width and height are still the default value.

camera="false": overrides ALL default properties. No camera can match those constraints so no camera is request in the first place. You can use this to turn of the camera at runtime.

camera="{}": since an empty object does not contain properties that could override something, this is just like falling back to the default. The same as not using the camera prop at all or passing undefined/null.

camera="true": overrides ALL default properties. You will accept any camera type there is. Not recommended though as iOS seems to have trouble when the height and width constraints are missing.

If you change this property after initialization, a new camera stream has to be requested and the init event will be emitted again.

Installation

yarn add vue-qrcode-reader

or using NPM:

npm install --save vue-qrcode-reader

Default import

Register component globally:

import Vue from 'vue'
import VueQrcodeReader from 'vue-qrcode-reader'

Vue.use(VueQrcodeReader)

Register locally in other components scope:

import Vue from 'vue'
import { QrcodeReader } from 'vue-qrcode-reader'

Vue.component('my-component', {
  components: { QrcodeReader },

  // ...
)

⚠️ A css file is included when importing the package. You may have to setup your bundler to embed the css in your page.

Browser

All the examples on the demo page utilize single-file components. To use them in your project you need a build tool like webpack. Check out #35 for a simpler example you can use right in the browser.

Besides Vue you need to include the following CSS and JS file:

• <link href="vue-qrcode-reader.css" rel="stylesheet">
• <script src="vue-qrcode-reader.browser.js"></script>

The plugin should be auto-installed. If not, you can install it manually.

Register component globally:

Vue.use(VueQrcodeReader)

Register locally in other components scope:

Vue.component('my-component', {
  components: {
    'qrcode-reader': VueQrcodeReader.QrcodeReader
  },

  // ...
)