How to Build Web Barcode Scanner Using React and Webcam

Someone asked me how to create a real-time web barcode scanning app with a webcam. Is it hard to implement it? I’ve written an article sharing how to integrate Dynamsoft JavaScript Barcode Reader SDK into a React project. The remaining work is to make a webcam component.  Since there is an open source project called react-webcam, we don’t need to reinvent the wheel. In this article, I will share how to build a web barcode scanner step by step.

Camera-based Web Barcode Scanning Component

Download and open react-webcam.js.

Find render() function to add a button and a canvas. We use the button to trigger barcode scan and render barcode results on the canvas:

render() {
    return (
      <div id='videoview' width={this.props.width} height={this.props.height}>
        <button onClick={this.scanBarcode}>Scan Barcodes</button>
        <video
          autoPlay
          width={this.props.width}
          height={this.props.height}
          src={this.state.src}
          muted={this.props.audio}
          className={this.props.className}
          playsInline
          style={this.props.style}
          ref={(ref) => {
            this.video = ref;
          }}
        />
        <canvas id="overlay" width={this.props.width} height={this.props.height}></canvas>
      </div>
    );
  }

To show the results on the video, we need to adjust the styles of the HTML elements. Create a react-webcam.css file:

#videoview {
    position: relative;
    width: 640px;
    height: 480px;
  }

#video {
    position: relative;
    width: 100%;
    height: 100%;
    z-index: 1
}

#overlay {
    position: absolute;
    top: 100;
    left: 0;
    width: 100%;
    height: 100%;
    z-index: 2
}

Import the CSS file in the react-webcam.js file:

import React, { Component } from 'react';
import PropTypes from 'prop-types';
import './react-webcam.css';

Create a scanBarcode() function, in which we need to get the byte array of the video frame and then call the decodeBuffer() method:

scanBarcode() {
    if (window.reader) {
      let canvas = document.createElement('canvas');
      canvas.width = this.props.width;
      canvas.height = this.props.height
      let ctx = canvas.getContext('2d');
      ctx.drawImage(this.video, 0, 0, this.props.width, this.props.height);
    
      window.reader.decodeBuffer(
        ctx.getImageData(0, 0, canvas.width, canvas.height).data,
        canvas.width,
        canvas.height,
        canvas.width * 4,
        window.dynamsoft.BarcodeReader.EnumImagePixelFormat.IPF_ARGB_8888
      )
      .then((results) => {
        this.showResults(results);
      });
    }
    
  }

How to make the window.reader initialized? In public/index.html, create the instance of the barcode reader and make it globally accessible once the wasm file is loaded:

<body>
    <img src="loading.gif" style="margin-top:10px" id="anim-loading">
    <script src="https://demo.dynamsoft.com/dbr_wasm/js/dbr-6.4.1.3.min.js"></script>
    <script>
      dynamsoft.dbrEnv.resourcesPath = 'https://demo.dynamsoft.com/dbr_wasm/js';
      dynamsoft.dbrEnv.onAutoLoadWasmSuccess = function () {
        window.reader = new dynamsoft.BarcodeReader();
        window.dynamsoft = dynamsoft;
        document.getElementById('anim-loading').style.display = 'none';
      };
      dynamsoft.dbrEnv.onAutoLoadWasmError = function (ex) {
        document.getElementById('anim-loading').style.display = 'none';
        alert('Fail to load the wasm file.');
      };
      dynamsoft.dbrEnv.bUseWorker = true;

      // Get a free trial license from https://www.dynamsoft.com/CustomerPortal/Portal/TrialLicense.aspx
      dynamsoft.dbrEnv.licenseKey = "Your Barcode SDK License"

    </script>
    <div id="root"></div>

Note: dynamsoft.dbrEnv.bUseWorker has to be true. If we do not use web worker, the main thread will be heavily blocked.

To make this work in scanBarcode(), bind it in the constructor:

constructor() {
    super();
    this.state = {
      hasUserMedia: false,
    };

    this.scanBarcode = this.scanBarcode.bind(this);
  }

The following code shows how to continuously scan and show the barcode results on the webcam video:

showResults(results) {
    let context = this.clearOverlay();
    let txts = [];
    try {
      let localization;
      for (var i = 0; i < results.length; ++i) {
        if (results[i].LocalizationResult.ExtendedResultArray[0].Confidence >= 30) {
          txts.push(results[i].BarcodeText);
          localization = results[i].LocalizationResult;
          this.drawResult(context, localization, results[i].BarcodeText);
        }
      }
      
      this.scanBarcode();
      
    } catch (e) {
      this.scanBarcode();
    }
  }

clearOverlay() {
    let context = document.getElementById('overlay').getContext('2d');
    context.clearRect(0, 0, this.props.width, this.props.height);
    context.strokeStyle = '#ff0000';
    context.lineWidth = 5;
    return context;
  }
  
drawResult(context, localization, text) {
    context.beginPath();
    context.moveTo(localization.X1, localization.Y1);
    context.lineTo(localization.X2, localization.Y2);
    context.lineTo(localization.X3, localization.Y3);
    context.lineTo(localization.X4, localization.Y4);
    context.lineTo(localization.X1, localization.Y1);
    context.stroke();
  
    context.font = '18px Verdana';
    context.fillStyle = '#ff0000';
    let x = [ localization.X1, localization.X2, localization.X3, localization.X4 ];
    let y = [ localization.Y1, localization.Y2, localization.Y3, localization.Y4 ];
    x.sort(function(a, b) {
      return a - b;
    });
    y.sort(function(a, b) {
      return b - a;
    });
    let left = x[0];
    let top = y[0];
  
    context.fillText(text, left, top + 50);
  }

Open App.js to add the React webcam component:

import React, { Component } from 'react';
import logo from './logo.svg';
import './App.css';
import {Barcode} from './Barcode';
import Webcam from './react-webcam';

class App extends Component {
  render() {
    return (
      <div className="App">
        <Barcode/>
        <Webcam />
      </div>
    );
  }
}

export default App;

Run the web barcode scanner app:

npm start

Visit localhost:3000:

react web barcode scanner with webcam

Source Code

https://github.com/dynamsoft-dbr/javascript-barcode/tree/master/examples/react-wasm-barcode