How to Use JavaScript Barcode SDK in AngularDart Project

AngularDart, similar to Angular built with TypeScript, is a web app framework written in Dartlang. It finally compiles to JavaScript.  In this article, I will share how to use Dynamsoft JavaScript Barcode SDK to create a simple web barcode reader app using AngularDart on Windows 10.

What You Should Know

Download and Installation

    pub global activate webdev
    pub global activate stagehand

Building Web Barcode Reader in AngularDart

Create a new project:

mkdir barcode
cd barcode
stagehand web-angular
pub get

Here is the project view in Visual Studio Code.

AngularDart project

By default, the template contains a to-do list component. It is useless, just delete it. After that, clean up the project:

  1. Open lib/app_component.html to delete <todo-list></todo-list>.
  2. In lib/app_component.dart, remove import ‘src/todo_list/todo_list_component.dart’ and directives: [TodoListComponent].

It is time to write my code. Open web/index.html to include the JS barcode library and add the initialization code:

<!DOCTYPE html>
<html>
  <head>
    <title>barcode</title>
    <meta charset="utf-8">
    <meta name="viewport" content="width=device-width, initial-scale=1">
    <link rel="stylesheet" href="styles.css">
    <link rel="icon" type="image/png" href="favicon.png">
    <img src="loading.gif" style="margin-top:10px" id="anim-loading">
    <script src="https://demo.dynamsoft.com/dbr\_wasm/js/dbr-6.4.1.0.min.js"></script>
    <script defer src="main.dart.js"></script>
    <script>
        dynamsoft.dbrEnv = dynamsoft.dbrEnv || {};
        dynamsoft.dbrEnv.resourcesPath = 'https://demo.dynamsoft.com/dbr\_wasm/js';
        //https://www.dynamsoft.com/CustomerPortal/Portal/TrialLicense.aspx
        dynamsoft.dbrEnv.licenseKey =
          't0068NQAAAJUlQ1oDc6zPWxOAQWn7kD9EGtgZFIqK/k3ULJC5ccG9Xe/lpVOxod82bm6nXxqQXUpC1zjRXU514mWw9XLE1JM=';
        dynamsoft.dbrEnv.bUseWorker = false;
        dynamsoft.dbrEnv.onAutoLoadWasmSuccess = function() {
          document.getElementById('anim-loading').style.display = 'none';
        };
        dynamsoft.dbrEnv.onAutoLoadWasmError = function(ex) {
          alert(ex);
        };
    </script>
  </head>
  <body>
    <my-app>Loading...</my-app>
  </body>
</html>

Add an HTMLInputElement and an HTMLDivElement to lib/app_component.html:

<h1>{{title}}</h1>
<div>
    <input id="uploadImage" type="file" accept="image/bmp,image/jpeg,image/png,image/gif" (input)="readBarcode()">
</div>
<div><b>Barcode result:</b> <span id='barcodeResults'>{{results}}</span></div>

Now let’s do some tricky things in lib/app_component.dart.

To interop JavaScript with Dart, we can import ‘package:js/js.dart’:

@JS()
library app_component;

import 'package:js/js.dart';

To make the package work, add dependency js: ^0.6.0 in pubspec.yaml:

dependencies:
  angular: ^5.1.0
  angular_components: ^0.10.1
  js: ^0.6.0

Declare the JavaScript barcode class and the decoding method:

import 'dart:js';
import 'dart:html';
import 'dart:convert';

@JS("dynamsoft.BarcodeReader")
class DynamsoftBarcodeReader {
  external factory DynamsoftBarcodeReader();
  external Promise<JsArray> decodeFileInMemory(File file);
}

Initialize the object:

class AppComponent implements OnInit {
  
  final title = 'Angular Dart - Barcode Reader';
  String results = '';
  DynamsoftBarcodeReader reader;

  void ngOnInit() async {
    results = '';
    reader = new DynamsoftBarcodeReader();
  }
}

Create a readBarcode() function binding with the HTMLInputElement:

void readBarcode() {
    InputElement input = document.querySelector('#uploadImage');
    FileList files = input.files;
    File file = files.item(0);

    if (reader != null) {
      reader.decodeFileInMemory(file).then(
        allowInterop(getResults)
      );
    } else {
      results = file.name;
    }
  }

The decodeFileInMemory method returns a Promise object, so we need to declare it as follows:

class Promise<T> {
  external Promise then(Function(T result));
}

The getResults() is a callback function for showing results:

void getResults(JsArray barcodes) {
    int len = barcodes.length;
    var json = jsonDecode(stringify(barcodes));
    var tmp = '';
    for (int i = 0; i < len; i++) {
      tmp += json\[i\]\['BarcodeText'\] + '; ';
    }

    SpanElement spanElement= document.querySelector('#barcodeResults');
    spanElement.text = tmp;
  }

Run the app:

webdev serve

If the port is unavailable, kill the relevant process:

netstat -aon | findstr 8080
taskkill /f /pid <ProcessID>

AngularDart barcode reader

Source Code

https://github.com/yushulx/javascript-barcode/tree/master/examples/angular-dart

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