Expo ESC/POS

A React Native library for converting HTML to ESC/POS commands that support thermal printer image printing. This is especially useful when your thermal printer doesn't support Vietnamese text or other complex character sets.

Main Features

The primary feature of this library is to convert HTML content to ESC/POS commands that can be sent to thermal printers. This approach allows you to:

Print Vietnamese text (and other complex characters) on printers that don't natively support them
Generate QR codes and barcodes directly from HTML attributes
Create complex layouts using HTML/CSS and convert them to printer-compatible images
Support both 58mm and 80mm thermal printers

Installation

npm install expo-escpos
# or
yarn add expo-escpos

Usage

Basic HTML to ESC/POS Conversion

import { renderHtmlToImages } from 'expo-escpos';

const printReceipt = async () => {
  const html = `
    <html>
      <body>
        <h1>Receipt</h1>
        <p>Customer: John Doe</p>
        <p>Total: $25.50</p>
      </body>
    </html>
  `;

  try {
    const escPosData = await renderHtmlToImages(html, {
      model: "80", // "58" for 58mm or "80" for 80mm printers
      maxHeightToBreak: 1600 // Optional: max height before breaking into multiple images
    });

    // Send escPosData to your thermal printer
    await sendToPrinter(escPosData);
  } catch (error) {
    console.error('Failed to generate receipt:', error);
  }
};

QR Code Generation

To generate QR codes in your HTML, use the data-type="qrcode" attribute:

<!-- Basic QR Code -->
<div data-type="qrcode" data-text="https://example.com">QR Code</div>

<!-- QR Code with custom size -->
<div data-type="qrcode" data-text="Order #12345" data-size="200">Order QR</div>

<!-- QR Code with error correction level -->
<div 
  data-type="qrcode" 
  data-text="Important Data" 
  data-size="150" 
  data-error-correction="H">
  High Quality QR
</div>

QR Code Attributes:

data-type="qrcode" - Required to identify this as a QR code element
data-text - The text/URL to encode (uses element text content if not provided)
data-size - Size in pixels (default: 150)
data-error-correction - Error correction level: "L", "M", "Q", "H" (default: "M")

Barcode Generation

To generate barcodes (Code 128), use the data-type="barcode" attribute:

<!-- Basic Barcode -->
<div data-type="barcode" data-text="123456789">Barcode</div>

<!-- Barcode with custom dimensions -->
<div 
  data-type="barcode" 
  data-text="PRODUCT001" 
  data-width="300" 
  data-height="100">
  Product Code
</div>

Barcode Attributes:

data-type="barcode" - Required to identify this as a barcode element
data-text - The text to encode (uses element text content if not provided)
data-width - Width in pixels (default: 200)
data-height - Height in pixels (default: width/2)

Complete Example with QR Codes and Barcodes

const generateReceiptWithCodes = async () => {
  const html = `
    <!DOCTYPE html>
    <html>
    <head>
      <style>
        body { font-family: Arial, sans-serif; padding: 20px; text-align: center; }
        .header { margin-bottom: 20px; }
        .item { margin: 10px 0; padding: 10px; border-bottom: 1px dashed #000; }
        .codes { margin-top: 20px; }
      </style>
    </head>
    <body>
      <div class="header">
        <h1>STORE NAME</h1>
        <p>Receipt #12345</p>
        <p>Date: ${new Date().toLocaleDateString()}</p>
      </div>

      <div class="item">
        <p><strong>Product A</strong></p>
        <p>Price: $10.00</p>
        <!-- Product barcode -->
        <div data-type="barcode" data-text="PROD001" data-width="200" data-height="60"></div>
      </div>

      <div class="item">
        <p><strong>Product B</strong></p>
        <p>Price: $15.50</p>
        <!-- Another product barcode -->
        <div data-type="barcode" data-text="PROD002" data-width="200" data-height="60"></div>
      </div>

      <div class="codes">
        <p><strong>Scan for receipt details:</strong></p>
        <!-- QR code with receipt information -->
        <div 
          data-type="qrcode" 
          data-text="https://store.com/receipt/12345" 
          data-size="150"
          data-error-correction="M">
        </div>

        <p style="margin-top: 20px;"><strong>Order ID:</strong></p>
        <!-- Order barcode -->
        <div data-type="barcode" data-text="ORD12345" data-width="250" data-height="80"></div>
      </div>

      <div style="margin-top: 30px;">
        <p>Thank you for your purchase!</p>
      </div>
    </body>
    </html>
  `;

  try {
    const escPosData = await renderHtmlToImages(html, {
      model: "80",
      maxHeightToBreak: 1600
    });

    // Send to printer via TCP, Bluetooth, or USB
    await sendToPrinter(escPosData);
  } catch (error) {
    console.error('Print failed:', error);
  }
};

API Reference

`renderHtmlToImages(html, options)`

Converts HTML content to ESC/POS commands for thermal printing.

Parameters:

html (string): The HTML content to convert
options (object):
- model (string): Printer model - "58" for 58mm or "80" for 80mm printers
- maxHeightToBreak (number, optional): Maximum height in pixels before breaking into multiple images (default: 1600)

Returns: Promise<Uint8Array> - ESC/POS command data ready to send to printer

`renderImages(config, imageBase64s)`

Converts base64 image strings directly to ESC/POS commands.

Parameters:

config (object):
- model (string): Printer model - "58" | "80"
imageBase64s (string[]): Array of base64-encoded image strings

Returns: Uint8Array - ESC/POS command data

Printer Communication

The library generates ESC/POS commands but doesn't handle printer communication. You'll need to send the data using:

TCP/IP: For network printers
Bluetooth: For Bluetooth printers
USB: For USB printers

Example TCP printing:

import TcpSocket from 'react-native-tcp-socket';

const sendToPrinter = async (data: Uint8Array, printerIP: string) => {
  return new Promise((resolve, reject) => {
    const client = TcpSocket.createConnection({
      port: 9100,
      host: printerIP
    }, () => {
      client.write(data, undefined, (error) => {
        client.destroy();
        if (error) reject(error);
        else resolve(true);
      });
    });

    client.on('error', reject);
    client.setTimeout(5000);
    client.on('timeout', () => reject(new Error('Connection timeout')));
  });
};

Supported Printer Models

58mm thermal printers (384px width)
80mm thermal printers (576px width)

Error Handling

The library includes comprehensive error handling for:

Invalid HTML content
QR code/barcode generation failures
Image processing errors
Memory management

Performance Tips

Optimize HTML: Keep HTML simple and avoid complex CSS
Image sizes: Use appropriate image sizes for your printer model
Break long receipts: Use maxHeightToBreak to split very long receipts
Test thoroughly: Always test with your specific printer model

License

MIT

Contributing

Contributions are welcome! Please feel free to submit a Pull Request.

Package detail

expo-escpos

readme