nodejs convert decimal to hex(00-00) and reverse? - node.js

Question

So I want to send a hex value to a service. The problem is that the service want this hex value in a specific format, 00-00, and also reversed.
For Example, when I want to tell the Service I want tag '1000':
1000 dec is 3E8 in hex. easy.
Now the service wants the format 03-E8.
Also the service reads from right to left so the final value would be E8-03.
Another example, '3' would be 03-00.
Edit:
I forgott to say that I dont need it as string, but as Uint8Array. So I would create the final result with new Uint8Array([232, 3]). (Eaquals E8-03 = 1000)
So the question in general is: How can I get a [232,3] from an input of 1000 or [3, 0] from 3?
Is there a build in methode or a pakage that already can do this convertion?

Answer 1

There's probably a much simpler way, but here is a simple solution.
Edit: If you need at least two pairs, you can change the first argument of padStart.
function dec2hexUi8Arr (n) {
const hex = (n).toString(16);
const len = hex.length;
const padLen = len + (len % 2);
const hexPad = hex.padStart(Math.max(padLen, 4), '0');
const pairs = hexPad.match(/../g).reverse().map(p => parseInt(p, 16));
const ui8Arr = new Uint8Array(pairs);
return ui8Arr;
}
const vals = [
1000,
3,
65536
].map(dec2hexUi8Arr);
console.log (vals);

Answer 2

I don't know any tool or package. I would do something like this:
const a = 1000;
const a0 = a % 256;
const a1 = Math.floor(a / 256);
const arr = new Uint8Array([a0, a1]);
console.log(arr);
const arrStr = []
arr.forEach((elem) => {
const str = elem.toString(16).toUpperCase();
if (str.length === 2) {
arrStr.push(str);
} else {
arrStr.push('0' + str)
}
});
console.log(arrStr.reverse().join('-'));
Output:
Uint8Array(2) [ 232, 3 ]
03-E8