Calculate Checksum For ASTM Frame

The structure of a frame is something like below

1[STX][F#][Text][ETX][CHK1][CHK2][CR][LF]

If the record is longer than the maximum number of characters, it is divided into 2 or more frames. The intermediate frame text termination code is [ETB], and the final frame text termination code is [ETX], as shown below

1[STX][F#][Text][ETB][CHK1][CHK2][CR][LF]
2[STX][F#][Text][ETB][CHK1][CHK2][CR][LF]
3......
4[STX][F#][Text][ETX][CHK1][CHK2][CR][LF]

[CHK1][CHK2] is expressed by characters "0" - "9" and "A" - "F". Characters beginning from the character following [STX] and until [ETB] or [ETX] (including [ETB] or [ETX]) are added in binary. The 2-digit numbers, which represent the least significant 8 bits in hexadecimal code, are converted to ASCII characters "0" - "9" and "A" - "F". The most significant digit is stored in CHK1 and the least significant digit in CHK2.

Suppose the frame is stored in input, we can calculate the cheksum as below

1function calculateChecksum(input) {
2  return input
3    .slice(1)
4    .split("")
5    .reduce((a, b) => a + b.charCodeAt(0), 0)
6    .toString(16)
7    .slice(-2)
8    .toUpperCase()
9    .padStart(2, "0");
10}
11
12var foo =
13  "\x021H|\\^&|||CT-90^00-15 ^00001^^^^BD934079||||||||E1394-97|20171104070923\x0D\x03";
14console.log(calculateChecksum(foo)); // '58'
15
16foo = "\x023O|1|||||20171104070923|||||N||||||||||||||F|||||\x0D\x03";
17console.log(calculateChecksum(foo)); // 'A4'