JaQR

A lightweight JavaScript utility module for creating a serverless dynamic QR code system and allows for user and QR code analytics

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Functions

getClientMetadata(req) · Node.js only

Extracts metadata from an incoming Node.js/Express request object.

Parameters

• req — A Node.js or Express request object.

Returns an object with:

Field	Description
signature	The JaQR query param value (trailing ~ stripped), or "" if absent
ip	Client IP address (respects x-forwarded-for)
device	User-Agent string, or "Unknown"
timestamp	Human-readable timestamp (MM/DD/YYYY, HH:MM AM/PM)

app.get('/track', (req, res) => {
  const meta = JaQR.getClientMetadata(req);
  console.log(meta);
  // { signature: 'a3f9...', ip: '192.168.1.1', device: 'Mozilla/5.0...', timestamp: '03/16/2026, 10:30 AM' }
});

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Get_Signature() · Browser only

Reads the JaQR query parameter from the current browser URL.

Returns the signature string of the QR code, or null if not present.

// URL: https://example.com/page?JaQR=a3f9b2~~
const sig = JaQR.Get_Signature();
// → 'a3f9b2'

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Sign_URL(url, metadata) · async

Appends a SHA-256 signature of metadata which can be appended with addtional info about the QR code, to a URL as the JaQR query parameter.

Parameters

• url (string) — The URL to sign.
• metadata (any) — Data to hash into the signature.

Returns a Promise<string> — the signed URL.

const signedURL = await JaQR.Sign_URL('https://example.com/scan', { userId: 42 });
// → 'https://example.com/scan?JaQR=7f83b...'

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Create_Signature(obj) · async

Produces a SHA-256 hex digest of any serializable object.

Parameters

• obj (any) — The value to hash (JSON-serialized before hashing).

Returns a Promise<string> — a 64-character hex string.

const hash = await JaQR.Create_Signature({ userId: 42, action: 'scan' });
// → '7f83b1657ff1fc53b92dc18148a1d65dfc2d4b1fa3d677284addd200126d9069'

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convertToSMSURI(obj)

Generates an SMS URI formatted for iOS or Android.

Parameters

• obj.tel (string) — Recipient phone number.
• obj.message (string) — Pre-filled message body.
• obj.device_OS (string) — "ios" or "android" (case-insensitive).

Returns a formatted sms: URI string, which can be provided to the client as a link

JaQR.convertToSMSURI({ tel: '+15551234567', message: 'Hello!', device_OS: 'ios' });
// → 'sms:+15551234567&body=Hello!'

JaQR.convertToSMSURI({ tel: '+15551234567', message: 'Hello!', device_OS: 'android' });
// → 'sms:+15551234567?body=Hello!'

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getVCardBytes(obj)

Generates a vCard 3.0 contact as a Uint8Array, suitable for file download or Blob creation.

Parameters

• obj.firstname (string)
• obj.lastname (string)
• obj.organization (string, optional)
• obj.email (string, optional)
• obj.phoneMobile (string, optional)

Returns a Uint8Array of the vCard content.

const bytes = JaQR.getVCardBytes({
  firstname: 'Jane',
  lastname: 'Doe',
  organization: 'Acme Corp',
  email: 'jane@acme.com',
  phoneMobile: '+15559876543'
});

// Browser download example:
const blob = new Blob([bytes], { type: 'text/vcard' });
const url = URL.createObjectURL(blob);

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convertToTelURI(obj)

Generates a tel: URI for initiating a phone call.

Parameters

• obj.tel (string) — The phone number.

Returns a tel: URI string, which can be provided to the client as a link

JaQR.convertToTelURI({ tel: '+15551234567' });
// → 'tel:+15551234567'

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convertToLocationURL(addr)

Generates a Google Maps search URL from an address object.

Parameters

• addr.street (string, optional)
• addr.city (string, optional)
• addr.state (string, optional)
• addr.zipcode (string, optional)
• addr.country (string, optional)

Returns a Google Maps URL string, which can be given to the client as a link

JaQR.convertToLocationURL({
  street: '1600 Amphitheatre Pkwy',
  city: 'Mountain View',
  state: 'CA',
  zipcode: '94043',
  country: 'USA'
});
// → 'https://www.google.com/maps/search/?api=1&query=1600+Amphitheatre+Pkwy%2C+Mountain+View%2C+CA%2C+94043%2C+USA'

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Environment Compatibility

Function	Node.js	Browser
getClientMetadata	✅	❌
Get_Signature	❌	✅
Sign_URL	✅	✅
Create_Signature	✅	✅
convertToSMSURI	✅	✅
getVCardBytes	✅	✅
convertToTelURI	✅	✅
convertToLocationURL	✅	✅

Sign_URL and Create_Signature require the crypto.subtle Web Crypto API, available natively in browsers and in Node.js v15+.

Usage

JaQR is a commonJS module and do not require any other external packages. So use as follows,

const JaQR = require('@monteluke/jaqr');

const metadata = JaQR.getClientMetadata(req);

This package is designed to be used along with the JaQR API which is under development by myself. It allows to create a redirect qr code of a url appended with unique signature, which can be used for QR code analytics (using Get_Signature function). The functions convertToSMSURI, getVCardBytes, convertToTelURI, convertToLocationURL can be used to create links and downloadable file (for getVCardBytes function), which can be provided to the client to trigger the necessary actions. The function getClientMetaData provide additional analytic capabilities about the client that enters through the redirect QR code. The actions triggered by using the functions is as follows,

Function	Action
convertToSMSURI	link opens the messages app with the given phone number and message
getVCardBytes	downloads a .vcf file which can be added to the contacts
convertToTelURI	link opens the dialer with the given phone number
convertToLocationURL	link opens google map to the given address

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Contributing & Maintenance

JaQR is a utility package maintained by the author. To keep the project scope focused and manageable, I am not currently accepting Pull Requests (PRs) or feature requests.

Feel free to fork the repository for your own personal use if you need to make modifications!