JSFiddle - React, Tailwind, and code Playground

JavaScript

var str = "45035997012373300";

var bytes = new Array(7);
for(var k=0;k<8;k++) {
    bytes[k] = mod256(str);
    str = divide256(str);
}
console.log(bytes);

function divide256(n)
{
    if (n.length <= 8)
    {
        return (Math.floor(parseInt(n) / 256)).toString();
    }
    else
    {
        var top = n.substring(0, n.length - 8);
        var bottom = n.substring(n.length - 8);
        var topVal = Math.floor(parseInt(top) / 256);
        var bottomVal = Math.floor(parseInt(bottom) / 256);
        var rem = (100000000 / 256) * (parseInt(top) % 256);
        bottomVal += rem;
        topVal += Math.floor(bottomVal / 100000000);
        bottomVal %= 100000000;
        if (topVal == 0) return bottomVal.toString();
        else return topVal.toString() + bottomVal.toString();
    }
}

function mod256(n)
{
    if (n.length <= 8)
    {
        return parseInt(n) & 255;
    }
    else
    {
        return parseInt(n.substring(n.length - 8)) & 255;
    }
}