Detect and Extract Barcodes - React JS

This tutorial shows how to create a React JS application that uses the LEADTOOLS SDK to perform barcode detection and recognition.

Summary This tutorial covers how to use LEADTOOLS Barcode SDK technology in a React JS application
Completion Time 30 minutes
Visual Studio Project Download tutorial project (209 KB)
Platform React JS Web Application
IDE Visual Studio : Service \ Visual Studio Code : Client
Development License Download LEADTOOLS
Try it in another language

Required Knowledge

Get familiar with the basic steps of creating a project by reviewing the Add References and Set a License and Display Images in an ImageViewer tutorials, before working on the Detect and Extract Barcodes - React JS tutorial.

Make sure that Yarn is installed so that creating a React application can be done quickly via the command line. If yarn is not installed, it can be found on:

Create the Project and Add LEADTOOLS References

To create the project structure open the command line console and cd into the location where the project is to be created. Then run the following command:

Yarn create react-app appname

The references needed depend upon the purpose of the project. For this project, the following JS files are needed:

Make sure to copy these files to the public\common folder and import them in the public\index.html file.

Set the License File

The License unlocks the features needed for the project. It must be set before any toolkit function is called. For details, including tutorials for different platforms, refer to Setting a Runtime License.

There are two types of runtime licenses:


Adding LEADTOOLS local references and setting a license are covered in more detail in the Add References and Set a License tutorial.

Import LEADTOOLS Dependencies

Open the index.html file in the public folder. Add the below necessary script tags inside the head to import LEADTOOLS dependencies.

  <meta charset="utf-8" /> 
  <link rel="icon" href="%PUBLIC_URL%/favicon.ico" /> 
  <meta name="viewport" content="width=device-width, initial-scale=1" /> 
  <meta name="theme-color" content="#000000" /> 
  <meta name="description" content="Web site created using create-react-app" /> 
<script src="" 
  integrity="sha256-CSXorXvZcTkaix6Yvo6HppcZGetbYMGWSFlBw8HfCJo=" crossorigin="anonymous"></script> 
  <!--Import LEADTOOLS dependencies--> 
  <script type="text/javascript" src="/common/Leadtools.js"></script> 
  <script type="text/javascript" src="/common/Leadtools.Controls.js"></script> 
  <script type="text/javascript" src="/common/Leadtools.Annotations.Engine.js"></script> 
  <script type="text/javascript" src="/common/Leadtools.Document.js"></script> 
  <!--Import our script with our Leadtools Logic--> 
  <script src="/common/app.js"></script> 
  <script src="/common/ltlogic.js"></script> 
  <link rel="manifest" href="%PUBLIC_URL%/manifest.json" /> 
  <title>React App</title> 

Add the DocumentHelper Class

With the project created, the references added, the ImageViewer initialized, and the license set, coding can begin.

Open ltlogic.js, this file should be situated in the Common folder in the public folder. Creation of ltlogic.js is covered in the Add References and Set a License tutorial. Add a new class called DocumentHelper after the set license call. Add the following code inside the new class.

class DocumentHelper { 
  static showServiceError = (jqXHR, statusText, errorThrown) => { 
    alert("Error returned from service. See the console for details."); 
    const serviceError = lt.Document.ServiceError.parseError(jqXHR, statusText, errorThrown); 
  static log = (message, data) => { 
    const outputElement = document.getElementById("output"); 
    if (outputElement) { 
      const time = (new Date()).toLocaleTimeString(); 
      const textElement = document.createElement("p"); 
      textElement.innerHTML = "\u2022" + " [" + time + "]: " + message; = "text-align: left;"; 
      outputElement.appendChild(textElement, outputElement.firstChild); 
    if (!data) 
      console.log(message, data); 

Open the App.js file in the src folder and replace the HTML with the following code:

import React from 'react'; 
import './App.css'; 
function App() { 
  return ( 
    <div className="App"> 
      <header className="App-header"> 
        <p id="serviceStatus"></p> 
        <h3>React Barcode Example </h3> 
        <div id="btnMenu"> 
        <input type="file" id="file-input" accept=".jpg,.jpeg,.png"></input> 
        <button id="addToViewer">Add Image To Viewer</button> 
        <button id="barcodeButton">Read Barcodes</button> 
        <div id="imageViewerDiv"></div> 
        <h6 id="output"></h6> 
export default App; 

Connect to the Document Service

In the public/common folder, add a blank app.js. Add the following contents to the file so the application can communicate with the LEADTOOLS Document Service.

var documentViewer, serviceStatus, output, exampleButton; 
// Parses error information. 
function showServiceError(jqXHR, statusText, errorThrown) { 
    alert("Error returned from service. See the console for details.") 
    var serviceError = lt.Document.ServiceError.parseError(jqXHR, statusText, errorThrown); 
// Startup function 
document.addEventListener("DOMContentLoaded", function () { 
    serviceStatus = document.getElementById("serviceStatus"); 
    output = document.getElementById("output"); 
    // To communicate with the DocumentsService, it must be running! 
    // Change these parameters to match the path to the service. 
    lt.Document.DocumentFactory.serviceHost = "http://localhost:40000"; 
    lt.Document.DocumentFactory.servicePath = ""; 
    lt.Document.DocumentFactory.serviceApiPath = "api"; 
    serviceStatus.innerHTML = "Connecting to service " + lt.Document.DocumentFactory.serviceUri; 
    .done(function (serviceData) { 
          let setStatus = function(){ 
            serviceStatus.innerHTML = ("\n" + "\u2022" + " Service connection verified!"); 
        setTimeout(setStatus, 1500); 
    .fail(function () { 
        serviceStatus.innerHTML = "Service not properly connected."; 

Improve the Visuals of the Project

Navigate to App.css, in the src folder which creates our HTML elements. Replace its contents with the following code to improve the visuals of the application.

.App { 
  text-align: center; 
@media (prefers-reduced-motion: no-preference) { 
  .App-logo { 
    animation: App-logo-spin infinite 20s linear; 
.App-header { 
  background-color: #282c34; 
  min-height: 100vh; 
  display: flex; 
  flex-direction: column; 
  align-items: center; 
  justify-content: center; 
  font-size: calc(10px + 2vmin); 
  color: white; 
.App-link { 
  color: #61dafb; 
@keyframes App-logo-spin { 
  from { 
    transform: rotate(0deg); 
  to { 
    transform: rotate(360deg); 
 background-color: #555555; 
 display: flex; 
 flex-direction: column; 
 width: 350px; 
 padding: 10px; 
  background-color: #888888; 
   width: 70%; 
   padding-left: 15px; 
   padding-right: 15px; 
  background-color: rgba(170, 170, 170, 1); 
  border-radius: 1%; 
  margin-top: 5px; 
  height: 400px; 
  width: 400px; 

Add the Barcode Read Code

Open ltlogic.js, and add the following code prior to the end of the window.onload() function.

  //Create an Image Viewer 
  let imageViewerDiv = document.getElementById("imageViewerDiv"); 
  const createOptions = new lt.Controls.ImageViewerCreateOptions(imageViewerDiv); 
  this.imageViewer = new lt.Controls.ImageViewer(createOptions); 
  this.imageViewer.zoom(, 1, imageViewer.defaultZoomOrigin); 
  this.imageViewer.viewVerticalAlignment =; 
  this.imageViewer.viewHorizontalAlignment =; 
  this.imageViewer.autoCreateCanvas = true; 
  this.imageViewer.imageUrl = ""; 
  //Create variables Grabbing the HTML elements 
  let fileList = document.getElementById("file-input"); 
  let btn = document.getElementById("addToViewer"); 
  btn.onclick = (function () { 
    //create our iterator 
    let i = 0; 
    //initially set our target to the first child of the uploaded files, then iterate it so 
    //subsequent images can be loaded in. 
    let files = fileList.files[i]; 
    let newUrl = window.URL.createObjectURL(files); 
    imageViewer.imageUrl = newUrl; 
  //Create the Barcode Button 
  var barcodeBtn = document.getElementById("barcodeButton"); 
  //Create the Click Event 
  barcodeBtn.onclick = (function () { 
    //Before running Barcode Recognition, we check if an image has been uploaded 
    let i = 0; 
    if (!fileList.files[i]) { 
      alert("No Image Chosen for Barcode Recognition. Select an Image via Choose File, before getting the Barcode"); 
    //Run Barcode Recognition on the Image 
      lt.Document.DocumentFactory.loadFromFile(fileList.files[i], new lt.Document.LoadDocumentOptions()) 
        .done((docum) => { 
          console.log("Document loaded and has cache id: " + docum.documentId); 
          //After making sure the file is loaded, Download it's document data. 
          lt.Document.DocumentFactory.downloadDocumentData(docum.documentId, null, false) 
            .done((result) => { 
              console.log("Finished downloading, mime type: " + result.mimeType + " data length: " +; 
              // Create a BLOB from this document 
              const data =; 
              const blob = new Blob([new Uint8Array(data, 0, data.byteLength)]); 
              console.log({ data }); 
              //here we are passing our blob into uploadDocument to put the binary data uploaded from the image into cache 
              const uploadDocumentOptions = new lt.Document.UploadDocumentOptions(); 
              uploadDocumentOptions.documentDataLength = blob.size; 
                .done((uploadUri) => { 
                  console.log(uploadUri, blob); 
                  lt.Document.DocumentFactory.uploadDocumentBlob(uploadUri, blob) 
                    .done(() => { 
                      console.log("finishing upload...") 
                        .done(() => { 
                          console.log("Loading document " + uploadUri); 
                          const options = new lt.Document.LoadDocumentOptions(); 
                          options.loadMode = lt.Document.DocumentLoadMode.localThenService; 
                          lt.Document.DocumentFactory.loadFromUri(uploadUri, options) 
                            .done((doc) => { 
                              //Now the Document is uploaded in cache, and we can verify by seeing it's Cache ID 
                              console.log("Document loaded and has cache id: " + doc.documentId); 
                              let leadRectD = lt.LeadRectD.empty; 
                              DocumentHelper.log("Barcode Recognition Starting..."); 
                              //Running Barcode Recognition on an image, Since appending the output to the bottom of the page elongates the document, we scroll to the output. 
                              let myelem = document.getElementById("output") 
                              let scrollOptions = { 
                                left: myelem.offsetParent.offsetWidth, 
                                top: myelem.offsetParent.offsetHeight, 
                                behavior: 'smooth' 
                                .done((CharacterData) => { 
                                  DocumentHelper.log("Barcode's value : " + CharacterData[0]._data); 

Run the Project

In order to run this application successfully, the LEADTOOLS .NET Framework Document Service is required. The LEADTOOLS .NET Framework Document Service project is located at <INSTALL_DIR>\LEADTOOLS21\Examples\JS\Services\DocumentServiceDotNet\fx.


Only the .NET FrameWork Document Service is able to uploadDocumentBlob, so this will not function with the .NET Core Document Service.

Open the DocumentService.csproj and run the project using IIS Express. After running the csproj Document Service project in Visual Studio, the webpage will show that the service is listening. The Client Side will be able to communicate with the Document Service, allowing the Image Data processing, and returning the Barcodes from the image.

Run Document service

Run the created barcode React application. Open the command line console and cd into the root of the project. From there, run yarn start. Choose a barcode image to extract the data from and select Add Image to Viewer.

Barcode image loaded

Select barcode and notice the results.

Barcode recognition result


This tutorial showed how to detect and extract barcode values.

See Also

Help Version 21.0.2023.3.1
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© 1991-2021 LEAD Technologies, Inc. All Rights Reserved.

Products | Support | Contact Us | Intellectual Property Notices
© 1991-2021 LEAD Technologies, Inc. All Rights Reserved.