TypeError: Cannot read property 'scan' of undefined scanner.js

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I am trying to integrate scanner-js in my react app but I receive the error TypeError: Cannot read property 'scan' of undefined.

You can find the code below:

import { scanner } from 'scanner-js';
class Home extends React.Component {
  constructor(props) {
    super(props);

    this.state = {};
  }

  scan = () => {
    scanner.scan(this.displayImagesOnPage, {
      output_settings: [
        {
          type: 'return-base64',
          format: 'jpg',
        },
      ],
    });
  };

  displayImagesOnPage(successful, mesg, response) {
    if (!successful) {
      // On error
      console.error('Failed: ' + mesg);
      return;
    }
    if (
      successful &&
      mesg != null &&
      mesg.toLowerCase().indexOf('user cancel') >= 0
    ) {
      // User cancelled.
      console.info('User cancelled');
      return;
    }
    var scannedImages = scanner.getScannedImages(response, true, false); // returns an array of ScannedImage
    for (
      var i = 0;
      scannedImages instanceof Array && i < scannedImages.length;
      i++
    ) {
      var scannedImage = scannedImages[i];
      var elementImg = scanner.createDomElementFromModel({
        name: 'img',
        attributes: {
          class: 'scanned',
          src: scannedImage.src,
        },
      });
    }
  }
  render() {
    return (
      <div>
        <button type="button" onClick={this.scan}>
          Scan
        </button>
      </div>
    );
  }
}

export default Home;

When I hover over the scanner object, the following things are showing, but I do not know why it's throwing an undefined error.

enter image description here

Can somebody help me to find the issue?

Thanks in advance.

reactjs javascript
1 Answers

It's because you're importing it wrong. If you check the package on npm, you can see that there is no exported module, so you can't import a single export (import {scanner} from 'scanner-js') nor you can import the default export (import scanner from 'scanner-js).

You need to import the entire module for side effects only, and it will add a global scanner variable to the window object.

import 'scanner-js';

console.log(typeof scanner);
// => object

console.log(typeof scanner.scan);
// => function

If you're using ESLint, you need to add scanner as a global variable.

CodeSandbox link: https://codesandbox.io/s/scanner-js-hcz2j

user_61263730
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