Develop Reference

Elegant way to split hex string at byte 00?

I need to split a hex string at every 00 byte. I tried this:
string.split('00');
But that causes splits at 5009, for instance, which is incorrect because it is splitting a byte in half.
In other words, it turns 5009 to [5, 9], which I don't want. But I do want it to turn af0059 to [af, 59].
Is it even possible to split bytes using regex, without cutting any bytes in half?
I could use a loop to seek through the string and only divide the string at even-number indices, but I would much prefer a regex expression.

Because of the byte sizes, you need to first split the string into byte-sizes, then map and finally join.
const string = "af00b9e00f70";
const res = string.split(/([\d\w]{4})/).filter(e => e).map(e => e.replace(/00([\d\w]{2})/, "$1").replace(/([\d\w]{2})00/, "$1")).join("");
console.log(res);

Here's a somewhat "old school' approach, but it demonstrates the principal. I say "old school' because we had to do this all the time back in the days of assembler coding. 'string' contains your long string of hex pairs (bytes). Here I convert it to byte values. Change the 'string' to whatever you want, but be sure it has an even number of hex digits. Call 'translate' to demonstrate it, and format the output into an alert() (or just output to the console)
var values = []; // output array
var string = "000102030405060708090a0b0c0d0e0f1FFFFEFDFCFBFAF9F8F7F6F5F4F3F2F0";
function getHexByteValues( string) {
var hex= "0123456789ABCDEF";
var outIx=0;
for (var i =0; i <= (string.length-2); i +=2) { // skip every other
//get higher and lower nibble
var hexdig1 = string.substring(i, i+1);
var hexdig0 = string.substring(i+1, i+2);
// for simplicity, convert alpha to upper case
hexdig1 = hexdig1.toUpperCase();
hexdig0 = hexdig0.toUpperCase();
// convert hex to decimal value.
// position in lookup string == value
var dec1 = hex.indexOf(hexdig1);
var dec0 = hex.indexOf(hexdig0);
// calc "byte" value, and add to values.
values[outIx++] = dec1 * 16 + dec0;
}
}
function translate(string) {
getHexByteValues(string);
var output="";
for (var i =0; i < values.length; i++) {
output += i + " = " + values[i] + "\r\n";
}
alert (output);
}

Maybe not the most elegant, but it works
const inp = "af00b9e00f70"
const out = inp.match(/.{1,2}/g).map(a=>a=="00"?"_":a).join("").split("_");
console.log(out);

JavaScript convert little endian string to number

I have a little piece of code that will convert a number to a 32 bit little endian string. That code is as follows.
var s = "";
var myNumber = 515
for(var i = 0; i < 32; i++){
var mask = 1 << i;
var bit = myNumber & mask;
s += bit ? "1" : "0"
}
console.log(s);
This works fine but I can't seem to figure out how I work back and convert the string back into it's orignal number. Can someone explain how to do this.

This is basically the same as your conversion to string, but reversed:
var num = 0;
for(let i = 0; i < s.length; i++) {
if (s[i] !== '0') {
num += 1 << i;
}
}
Or, you could convert the string to an array, reverse it, convert it back to a string, and call parseInt with a base of 2:
var num = parseInt(s.split('').reverse().join(''), 2);

Hex to Windows-1251 with JavaScript

I'm trying to convert a hexadecimal string to string with Windows-1251 encoding. I need to use JavaScript. I've tried using this sample that someone posted:
var win1251 = new TextDecoder("windows-1251");
for (var i = 0x00; i < 0xFF; i++) {
var hex = (i <= 0x0F ? "0" : "") + i.toString(16).toUpperCase();
decodeMap[hex] = win1251.decode(Uint8Array.from([i]));
}
but I can't seem to make it work. Can someone please help out?

Propably you're using it in incorrect way.
The code in you post creates dictionary (hex => windows-1251).
So, to translate hex string to windows-1251 string you have to:
split your hex string into array with 2-hex elements
Translate every element to windows-1251
Join result array into string
var decodeMap = {};
var win1251 = new TextDecoder("windows-1251");
for (var i = 0x00; i < 0xFF; i++) {
var hex = (i <= 0x0F ? "0" : "") + i.toString(16).toUpperCase();
decodeMap[hex] = win1251.decode(Uint8Array.from([i]));
}
var number = "3230313830363131313535303435303831";
var hexarr = number.toUpperCase().match(/[0-9A-F]{2}/g)
var win1251arr = hexarr.map(el=> decodeMap[el]);
console.log(win1251arr.join(""))
You can also do it in much shorter way (directly translate your hex string without creating dictionary):
var win1251 = new TextDecoder("windows-1251");
var number = "3230313830363131313535303435303831";
var arr = number.toUpperCase().match(/[0-9A-F]{2}/g).map(el=>"0x"+el);
var uarr = Uint8Array.from(arr);
console.log(win1251.decode(uarr));
If your browser doesn't support TextDecoder, you can use dictionary from first snippet:
var decodeMap = getHexToWin1251Dictionary();
var number = "3230313830363131313535303435303831";
var hexarr = number.toUpperCase().match(/[0-9A-F]{2}/g)
var win1251arr = hexarr.map(el=> decodeMap[el]);
console.log(win1251arr.join(""))
// function below returns content of decodeMap from first snippet
function getHexToWin1251Dictionary(){
return {"10":"\u0010","11":"\u0011","12":"\u0012","13":"\u0013","14":"\u0014","15":"\u0015","16":"\u0016","17":"\u0017","18":"\u0018","19":"\u0019","20":" ","21":"!","22":"\"","23":"#","24":"$","25":"%","26":"&","27":"'","28":"(","29":")","30":"0","31":"1","32":"2","33":"3","34":"4","35":"5","36":"6","37":"7","38":"8","39":"9","40":"#","41":"A","42":"B","43":"C","44":"D","45":"E","46":"F","47":"G","48":"H","49":"I","50":"P","51":"Q","52":"R","53":"S","54":"T","55":"U","56":"V","57":"W","58":"X","59":"Y","60":"`","61":"a","62":"b","63":"c","64":"d","65":"e","66":"f","67":"g","68":"h","69":"i","70":"p","71":"q","72":"r","73":"s","74":"t","75":"u","76":"v","77":"w","78":"x","79":"y","80":"Ђ","81":"Ѓ","82":"‚","83":"ѓ","84":"„","85":"…","86":"†","87":"‡","88":"€","89":"‰","90":"ђ","91":"‘","92":"’","93":"“","94":"”","95":"•","96":"–","97":"—","98":"","99":"™","00":"\u0000","01":"\u0001","02":"\u0002","03":"\u0003","04":"\u0004","05":"\u0005","06":"\u0006","07":"\u0007","08":"\b","09":"\t","0A":"\n","0B":"\u000b","0C":"\f","0D":"\r","0E":"\u000e","0F":"\u000f","1A":"\u001a","1B":"\u001b","1C":"\u001c","1D":"\u001d","1E":"\u001e","1F":"\u001f","2A":"*","2B":"+","2C":",","2D":"-","2E":".","2F":"/","3A":":","3B":";","3C":"<","3D":"=","3E":">","3F":"?","4A":"J","4B":"K","4C":"L","4D":"M","4E":"N","4F":"O","5A":"Z","5B":"[","5C":"\\","5D":"]","5E":"^","5F":"_","6A":"j","6B":"k","6C":"l","6D":"m","6E":"n","6F":"o","7A":"z","7B":"{","7C":"|","7D":"}","7E":"~","7F":"","8A":"Љ","8B":"‹","8C":"Њ","8D":"Ќ","8E":"Ћ","8F":"Џ","9A":"љ","9B":"›","9C":"њ","9D":"ќ","9E":"ћ","9F":"џ","A0":" ","A1":"Ў","A2":"ў","A3":"Ј","A4":"¤","A5":"Ґ","A6":"¦","A7":"§","A8":"Ё","A9":"©","AA":"Є","AB":"«","AC":"¬","AD":"­","AE":"®","AF":"Ї","B0":"°","B1":"±","B2":"І","B3":"і","B4":"ґ","B5":"µ","B6":"¶","B7":"·","B8":"ё","B9":"№","BA":"є","BB":"»","BC":"ј","BD":"Ѕ","BE":"ѕ","BF":"ї","C0":"А","C1":"Б","C2":"В","C3":"Г","C4":"Д","C5":"Е","C6":"Ж","C7":"З","C8":"И","C9":"Й","CA":"К","CB":"Л","CC":"М","CD":"Н","CE":"О","CF":"П","D0":"Р","D1":"С","D2":"Т","D3":"У","D4":"Ф","D5":"Х","D6":"Ц","D7":"Ч","D8":"Ш","D9":"Щ","DA":"Ъ","DB":"Ы","DC":"Ь","DD":"Э","DE":"Ю","DF":"Я","E0":"а","E1":"б","E2":"в","E3":"г","E4":"д","E5":"е","E6":"ж","E7":"з","E8":"и","E9":"й","EA":"к","EB":"л","EC":"м","ED":"н","EE":"о","EF":"п","F0":"р","F1":"с","F2":"т","F3":"у","F4":"ф","F5":"х","F6":"ц","F7":"ч","F8":"ш","F9":"щ","FA":"ъ","FB":"ы","FC":"ь","FD":"э","FE":"ю"};
}

How to add a common string in every randomly generated string Javascript

I am generating random strings using the below function in node.js. I wanted to know if there is any way to create text strings appropriately with a common string within every randomly generated string.
EDIT: The common string can be in any location of the generated string
For example:
Randomly generated string - Cxqtooxyy4
Can I add 'abc' or 'ABC' within that string like this - Cxqtoabcoxyy4 or CxqtoABCoxyy4 respectively.
My Code -
var randomTextArrayGeneration = function(size)
{
var text = "";
var possible = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789";
for(var i=0;i<size;i++)
text += possible.charAt(Math.floor(Math.random() * possible.length));
return text;
}
Can anyone tell me how do I do this? Any help is really helpful.

var n = text.length; //The size of your random string
var randomPosition = Math.floor((Math.random() * n) + 1); //Generate a random number between 1 and the size of your string
//Separate your string in 2 strings
var text1 = text.substring(1, randomPosition);
var text2 = text.substring(randomPosition, n);
//Create your final string by adding the common string between your two halves
var textFinal = text1 + commonString + text2;
return textFinal;
I don't remember how exactly works .substring(), you may want to change 1 by 0 in some places.

A rough sketch of the algorithm is this:
create random string of length size - <FIXED_STRING>.length
append <FIXED_STRING> to the end of generated string
Done.
A corner case is if size < <FIXED_STRING>.length, here you would need to provide some more discussion on what should happen.

You can use String.prototype.slice() to select 0-n characters from possible to insert into random index within string returned from randomTextArrayGeneration. If 0 is passed to randomTextArrayGeneration the selected string from possible will be set as result
var randomTextArrayGeneration = function(size, from, to) {
var text = "";
var possible = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789";
for (var i = 0; i < size; i++) {
text += possible.charAt(Math.floor(Math.random() * possible.length))
};
var len = Math.floor(Math.random() * text.length - 3);
var res = text.slice(0, len) + possible.slice(from, to).toLowerCase() + text.slice(len);
return res
}

javascript string algorithm

Let's say I have a string variable called myString, and another string variable called myChar.
var myString = "batuhan"; // it's user input.
var myChar = "0"; // will be one character, always
What I need is, a function that returns all the combinations of myString and myChar.
Like:
"batuhan","batuha0n","batuh0an","batuh0a0n","batu0han","batu0ha0n","batu0h0an","batu0h0a0n","bat0uhan","bat0uha0n","bat0uh0an","bat0uh0a0n","bat0u0han","bat0u0ha0n","bat0u0h0an","bat0u0h0a0n","ba0tuhan","ba0tuha0n","ba0tuh0an","ba0tuh0a0n","ba0tu0han","ba0tu0ha0n","ba0tu0h0an","ba0tu0h0a0n","ba0t0uhan","ba0t0uha0n","ba0t0uh0an","ba0t0uh0a0n","ba0t0u0han","ba0t0u0ha0n","ba0t0u0h0an","ba0t0u0h0a0n","b0atuhan","b0atuha0n","b0atuh0an","b0atuh0a0n","b0atu0han","b0atu0ha0n","b0atu0h0an","b0atu0h0a0n","b0at0uhan","b0at0uha0n","b0at0uh0an","b0at0uh0a0n","b0at0u0han","b0at0u0ha0n","b0at0u0h0an","b0at0u0h0a0n","b0a0tuhan","b0a0tuha0n","b0a0tuh0an","b0a0tuh0a0n","b0a0tu0han","b0a0tu0ha0n","b0a0tu0h0an","b0a0tu0h0a0n","b0a0t0uhan","b0a0t0uha0n","b0a0t0uh0an","b0a0t0uh0a0n","b0a0t0u0han","b0a0t0u0ha0n","b0a0t0u0h0an","b0a0t0u0h0a0n"
Rules: myChar shouldn't follow myChar
How can I do that? Really my brain dead right now :/

It's possible to implement what you want using recursion.
// Example: allCombinations("abcd", "0") returns the array
// ["abcd", "abc0d", "ab0cd", "ab0c0d", "a0bcd", "a0bc0d", "a0b0cd", "a0b0c0d"]
function allCombinations(str, chr) {
if (str.length == 1)
return [str];
var arr = allCombinations(str.substring(1), chr);
var result = [];
var c = str.charAt(0);
for (var i = 0; i < arr.length; i++)
result.push(c + arr[i]);
for (var i = 0; i < arr.length; i++)
result.push(c + chr + arr[i]);
return result;
}

You may or may not have noticed this but this is basically counting in binary. If we define bit 0 to be the absence of myChar and bit 1 to be the presence of myChar, then the following sequence:
var myString = ".....";
var myChar = "1";
var sequence = [
".....1",
"....1.",
"....1.1",
"...1.."
];
is basically counting from 1 to 4 in binary:
var sequence = [
0b0000001,
0b0000010,
0b0000011,
0b0000100
];
Therefore, all you need is a for loop to count up to the bit amount of the length of the string plus 1 (because the position at the end of the string is also legal):
var len = Math.pow(2,myString.length+1);
for (var x = 0; x < len; x++) {
// x in binary is all the possible combinations
// now use the "1" bits in x to modify the string:
// Convert myString to array for easy processing:
var arr = myString.split('');
arr.push(""); // last position;
for (var i = myString.length; i >= 0; i--) {
if ((x >> i) & 0x01) { // check if bit at position i is 1
arr[i] = myChar + arr[i];
}
}
console.log(arr.join('')); // print out one combination
}
Of course, this works only for small strings of up to 31 characters. For larger strings you'd need to do the binary counting using things other than numbers. Doing it in a string form is one option. Another option is to use a bigint library such as BigInteger.js to do the counting.