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JavaScript Hello World Sample - React

React is a JavaScript library meant explicitly for creating interactive UIs. Follow this guide to learn how to implement Dynamsoft Barcode Reader JavaScript SDK (hereafter called “the library”) into a React application.

Official Sample

Preparation

Make sure you have node and yarn installed. node 14.16.0 and yarn 1.22.10 are used in the example below.

Create the sample project

Create a Bootstrapped Raw React Application

npx create-react-app read-video-react

CD to the root directory of the application and install the dependencies

yarn add dynamsoft-javascript-barcode

Start to implement

Add a file “dbr.js” under “/src/” to configure the library

import DBR from "dynamsoft-javascript-barcode";
DBR.BarcodeReader.engineResourcePath = "https://cdn.jsdelivr.net/npm/dynamsoft-javascript-barcode@8.4.0/dist/";
export default DBR;

Note:

There are multiple settings available for the configuration, here we only set the engineResourcePath which is essential for the library to get the necessary resources at runtime.

Create a directory “components” under “/src/” and create the following files inside it to represent two components

BarcodeScanner.js
HelloWorld.css
HelloWorld.js

Edit the BarcodeScanner component

In BarcodeScanner.js, add code for initializing and destroying the library.

import DBR from "../dbr";
import React from 'react';

class BarcodeScanner extends React.Component {
    constructor(props) {
        super(props);
        this.bDestroyed = false;
        this.pScanner = null;
        this.elRef = React.createRef();
    }
    async componentDidMount() {
        try {
            let scanner = await (this.pScanner = this.pScanner || DBR.BarcodeScanner.createInstance());
            if (this.bDestroyed) {
                scanner.destroy();
                return;
            }
            this.elRef.current.appendChild(scanner.getUIElement());
            await scanner.open();
        } catch (ex) {
            console.error(ex);
        }
    }
    async componentWillUnmount() {
        this.bDestroyed = true;
        if (this.pScanner) {
            (await this.pScanner).destroy();
        }
    }
    shouldComponentUpdate() {
        // Never update UI after mount, dbrjs sdk use native way to bind event, update will remove it.
        return false;
    }
    render() {
        return (
            <div style= ref={this.elRef}>
            </div>
        );
    }
}

export default BarcodeScanner;

Note:
The html code in render() and the following code builds the UI for the library.
this.elRef.current.appendChild(scanner.getUIElement());
To release resources timely, the BarcodeScanner instance is destroyed with the component in the callback componentWillUnmount.

The component should never update (check the code for shouldComponentUpdate()) so that events bound to the UI stay valid.

Edit the HelloWorld component

Add the BarcodeScanner component in HelloWorld.js

import './HelloWorld.css';
import React from 'react';
import BarcodeScanner from './BarcodeScanner';

class HelloWorld extends React.Component {
    constructor(props) {
        super(props);
    }
    render() {
        return (
            <div id="UIElement">
                <BarcodeScanner></BarcodeScanner>
            </div>
        );
    }
}
export default HelloWorld;

Define the style of the element in HelloWorld.css

#UIElement {
    margin: 2vmin auto;
    text-align: center;
    font-size: medium;
    height: 40vh;
    width: 80vw;
}

Add the HelloWorld component to `App.js`

Edit the file App.js to be like this

import './App.css';
import HelloWorld from './components/HelloWorld.js';

function App() {
  return (
    <div className="App">
      <HelloWorld></HelloWorld>
    </div>
  );
}

export default App;

Try running the project.

yarn start

If you followed all the steps correctly, you will have a working page that turns one of the cameras hooked to or built in your computer or mobile device into a barcode scanner. However, the found barcodes are not displayed anywhere yet. At the same time, there is a short delay for the initialization of the library during which nothing happens and is not user-friendly. The following takes care of these two issues.

Update `HelloWorld.js`

Add state values

constructor(props) {
    super(props);
    this.state = {
        libLoaded: false,
        resultValue: "",
        bShowScanner: false
    };
}

Add a few functions

import DBR from "../dbr";

async componentDidMount() {
    try {
        //Load the library on page load to speed things up.
        await DBR.BarcodeScanner.loadWasm();
        this.setState(state => {
            state.libLoaded = true;
            return state;
        }, () => {
            this.showScanner();
        });
    } catch (ex) {
        alert(ex.message);
        throw ex;
    }
}    
showScanner = () => {
    this.setState({
        bShowScanner: true
    });
}
appendMessage = (message) => {
    switch (message.type) {
        case "result":
            this.setState(prevState => {
                prevState.resultValue = message.format + ": " + message.text;
                return prevState;
            });
            break;
        case "error":
            this.setState(prevState => {
                prevState.resultValue = message.msg;
                return prevState;
            });
            break;
        default: break;
    }
}

NOTE :

The method loadWasm() in the function componentDidMount() initializes the library in the background. The scanner UI is only shown when the initialization finishes.

The method appendMessage() is used to show the result text on the page.

Change the UI

render() {
    return (
        <div className="helloWorld">
            <div id="UIElement">
                {!this.state.libLoaded ? (<span style=>Loading Library...</span>) : ""}
                {this.state.bShowScanner ? (<BarcodeScanner appendMessage={this.appendMessage}></BarcodeScanner>) : ""}
            </div>
            <input type="text" value={this.state.resultValue} readOnly={true} id="resultText" />
        </div>
    );
}

Add style for the “input” element in HelloWorld.css

#resultText {
    display: block;
    margin: 0 auto;
    padding: 0.4rem 0.8rem;
    color: inherit;
    width: 80vw;
    border: none;
    font-size: 1rem;
    border-radius: 0.2rem;
    text-align: center;
}

In BarcodeScanner.js, use the event onFrameRead and the parent method appendMessage() to return the results.

async componentDidMount() {
  try {
      //Omitted code...
      scanner.setUIElement(this.elRef.current);
      scanner.onFrameRead = results => {
          for (let result of results) {
              this.props.appendMessage({ format: result.barcodeFormatString, text: result.barcodeText, type: "result" });
              if (result.barcodeText.indexOf("Attention(exceptionCode") !== -1) {
                  this.props.appendMessage({ msg: result.exception.message, type: "error" });
              }
          }
      };
      await scanner.open();
  } catch (ex) {
      this.props.appendMessage({ msg: ex.message, type: "error" });
      console.error(ex);
  }
}

NOTE :

The event onFrameRead is triggered upon reading of each frame. If barcodes are found on that frame, the results will be returned and shown on the page.

After the above changes, the application is made more user-friendly and the barcode text is displayed on the page right away. You can start implementing your own business workflow and make the application useful.