EAN8 to EPC and EPC to EAN8 produces different results

[dim2k2006]

As far as I understand if I encode EAN8 value to EPC and then decode this EPC back to EAN I should get the original EAN value but this never happens.

Example of code:

`
const epcToEan = (epc: string): string => {
const data = tds.valueOf(epc);

const result = data.toBarcode() as string;

return result;
};

const eanToEpc = (ean: string): string => {
const epc = new tds.Sgtin96().setGtin(ean);

return epc.toHexString();
};

console.log('eanToEpc -> epcToEan:', epcToEan(eanToEpc('60573421')));
`

I was expecting to receive 60573421 as a result but I receive 60000005734216.

What am I doing wrong?

[sergiss]

Hi Dmitry,

Thanks for your input.

GS1 documentation indicates that a GTIN must have 14 digits, so the user must fill in with leading zeros.

Try this:

console.log('eanToEpc -> epcToEan:', epcToEan(eanToEpc('00000060573421')));

Or modify your eanToEpc method, like this:

const eanToEpc = (ean: string): string => {
const epc = new tds.Sgtin96().setGtin(ean.padStart(14,"0"));
return epc.toHexString();
}

You can also use this GS1 web app to perform checks:

https://www.gs1.org/services/epc-encoderdecoder

Best regards.

Sergi

[dim2k2006]

Aha, and then when I receive a result from RFID device (which is EPC) and extract EAN from it, I can safely remove all leading zeros from this EAN?

[sergiss]

Yes, you can remove them, but if you want to use a standard later (GTIN-8, GTIN-12, GTIN-14), you will have to control the number of digits.

[dim2k2006]

Got it, thank you so much for the library and for the information!)

[dim2k2006]

Hello,

I use the same logic ean -> epc -> ean and seems like there is something wrong with some ean numbers:

original ean: 00000074018029. decoded ean: 00000074018024. epc: 30000001C3C5280000000000
original ean: 00000045214445. decoded ean: 00000045214448. epc: 3000000113F7900000000000
original ean: 00000028225773. decoded ean: 00000028225775. epc: 30000000AC46C40000000000

The last digit in decoded ean differs from the original ean number.

What could be the reason for such behavior?

[sergiss]

Hello Dmitry,
The EAN codes you are using have the wrong control code. For example, the ean 0000007401802(4) has 4 as check digit.
Greetings.

[dim2k2006]

I checked all the above eans here https://www.gs1.ch/en/home/offer/barcode/check-digit-calculator-and-ean-13-barcode-generator and yes all of them have the wrong check digit. Thank you so much for pointing it out!)