Added utility to calculate EAN barcode type parity bit #56

Author: uyu423

.gitignore

@@ -3,4 +3,5 @@ node_modules
 *.sublime*
 psd
 thumb
-*.log
+*.log
+package-lock.json

barcode.js

@@ -0,0 +1,21 @@
+'use strict';
+
+function getParityBit(code, type) {
+  switch(type) {
+    case 'EAN13':
+    case 'EAN8': {
+      var parity = 0, reversedCode = code.split('').reverse().join('');
+      for (var counter = 0; counter < reversedCode.length; counter += 1) {
+        parity += parseInt(reversedCode.charAt(counter), 10) * Math.pow(3, ((counter + 1) % 2));
+      }
+      return String((10 - (parity % 10)) % 10);
+    }
+    default: {
+      return '';
+    }
+  }
+}
+
+module.exports = {
+  getParityBit,
+};

examples/barcode.js

@@ -0,0 +1,20 @@
+'use strict';
+const escpos = require('../');
+
+const device  = new escpos.USB();
+
+const printer = new escpos.Printer(device);
+
+device.open(function() {
+  printer
+  .font('a')
+  .align('ct')
+  .size(1, 1)
+  .text('EAN13 barcode example')
+  .barcode('123456789012', 'EAN13') // code length 12
+  .barcode('109876543210') // default type 'EAN13'
+  .barcode('7654321', 'EAN8') // The EAN parity bit is automatically added.
+  .cut()
+  .cut()
+  .close();
+});

examples/index.js

@@ -16,7 +16,7 @@ device.open(function(){
   .size(1, 1)
   .text('The quick brown fox jumps over the lazy dog')
   .text('敏捷的棕色狐狸跳过懒狗')
-  .barcode('12345678', 'EAN8')
+  .barcode('1234567', 'EAN8')
   .qrimage('https://github.com/song940/node-escpos', function(err){
     this.cut();
     this.close();

printer.js

@@ -6,6 +6,7 @@ const getPixels    = require('get-pixels');
 const Buffer       = require('mutable-buffer');
 const EventEmitter = require('events');
 const Image        = require('./image');
+const Barcode      = require('./barcode');
 const _            = require('./commands');
 
 /**
@@ -277,6 +278,8 @@ Printer.prototype.hardware = function(hw){
  * @return printer instance
  */
 Printer.prototype.barcode = function(code, type, width, height, position, font){
+  var convertCode = String(code);
+  var parityBit = ''
   if(width >= 2 || width <= 6){
     this.buffer.write(_.BARCODE_FORMAT.BARCODE_WIDTH[width]);
   }else{
@@ -296,7 +299,16 @@ Printer.prototype.barcode = function(code, type, width, height, position, font){
   this.buffer.write(_.BARCODE_FORMAT[
     'BARCODE_' + ((type || 'EAN13').replace('-', '_').toUpperCase())
   ]);
-  this.buffer.write(code);
+  if ((!type || type === 'EAN13') && convertCode.length != 12) {
+    throw Error('EAN13 Barcode type requires code length 12');
+  }
+  if (type === 'EAN8' && convertCode.length != 7) {
+    throw Error('EAN8 Barcode type requires code length 7');
+  }
+  if (!type || type === 'EAN13' || type === 'EAN8') {
+    parityBit = Barcode.getParityBit(code, type || 'EAN13');
+  }
+  this.buffer.write(code + parityBit);
   return this;
 };