Need help in correcting issues in CRC-ITU check method written in Javascript (node.js)

Question

We are trying to code GPS device listener on Javascript.

While doing this, we are unable to develop the right script for the CRC-ITU error check. The explanation for

Answer 1

The ~ in the original code only worked because it was a 16-bit type. You should use crcX = crcX ^ 0xffff instead of crcX = ~crcX.

Also your buf.substring(i,i+4) and i = i + 4 is wrong. You need to process one byte at a time, which is two hexadecimal digits. Those should both be i+2.