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decode from unicode hex to string

When I load my data from my model (asp.net model) if the string is in another language (Russian for example), I'm getting the unicode hex code of the chars. How can I convert them to a normal string?
The problem isn't from the javascript encoding, it's from loading it from the model. I tried using a lot of functions from the forum but none worked!
Here is an example of a value I should get:
Петър
And here is what I'm actually getting:
Петър

const sequence = 'Петър'
const charCode = sequence.split(/[;\s]+/g)
// remove empty
.filter((v) => v)
// &#x41F -> 0x41F -> number
.map((v) => Number.parseInt(v.replace(/&#/, '0')))
console.log(
String.fromCharCode(...charCode)
)

Parse Ascii Escaped String in JavaScript

Say we're given a string that itself contains ASCII escape characters, such as "\x64" (note that this is the contents of the string, not what it would be in code). Is there an easy way in JavaScript to parse this to its actual character?
There's the old trick of using JSON.parse but that seems to only work with unicode escape sequences and can't recognize ASCII ones, as in:
JSON.parse(`"\\u0064"`); // Output: "d" (as expected)
JSON.parse(`"\\x64"`); // ERROR: Unexpected token x
Is there an equivalent that would work for the ASCII escape sequence? I know that using eval() works but I'd really rather not use eval.
EDIT: To clarify, some characters in the original string may not be escaped; as we may need to parse "Hello Worl\x64", for instance.

One solution is to replace all the \x** patterns in the string, using a callback to parse them as base 16 integers and pass the result to String.fromCharCode to convert to a character:
const str = "\\x48\\x65ll\\x6f\\x20W\\x6f\\x72\\x6c\\x64";
const res = str.replace(/\\x(..)|./g, (m, p1) => p1 ? String.fromCharCode(parseInt(p1, 16)) : m);
console.log(res);
If you don't mind overwriting the original string, this can be simplified slightly to:
let str = "\\x48\\x65ll\\x6f\\x20W\\x6f\\x72\\x6c\\x64";
str = str.replace(/\\x(..)/g, (m, p1) => String.fromCharCode(parseInt(p1, 16)));
console.log(str);

You can use the eval function to evaluate a string in the same way it would be evaluated from Javascript source code, you'll only need to make sure you quote its content as such:
eval("\"\\x64\"") // will return the javascript string: "d"

Decoding not working with Base64

Encoding my URL works perfectly with base-64 encoding. So does decoding but not with the string literal variable.
This works:
document.write(atob("hi"));
This does not:
var tempvar = "hello";
document.write(atob(tempvar));
What am I doing wrong? Nothing is displayed. But if I quote "tempvar", then it of course works but is not the same thing since "tempvar" is a string, not a variable.

Your Question
What am I doing wrong?
The string being passed to atob() is a string literal of length 5 (and not technically a base-64 encoded string). The browser console should reveal an exception in the error log (see explanation in The cause below).
The cause
Per the MDN documentation of atob():
Throws
Throws a DOMException if the length of passed-in string is not a multiple of 4. 1
The length of the string literal "hello" (i.e. 5) is not a multiple of 4. Thus the exception is thrown instead of returning the decoded version of the string literal.
A Solution
One solution is to either use a string that has actually been encoded (e.g. with btoa()) or at least has a length of four (e.g. using String.prototype.substring()). See the snippet below for an example.
var tempvar = "hello";
window.addEventListener("DOMContentLoaded", function(readyEvent) {
var container = document.getElementById("container");
//encode the string
var encoded = btoa(tempvar);
container.innerHTML = encoded;
var container2 = document.getElementById("container2");
//decode the encoded string
container2.innerHTML = atob(encoded);
var container3 = document.getElementById("container3");
//decode the first 4 characters of the string
container3.innerHTML = atob(tempvar.substring(0, 4));
});
<div> btoa(tempvar): <span id="container"></span></div>
<div> atob(decoded): <span id="container2"></span></div>
<div> atob(tempvar.substring(0, 4)): <span id="container3"></span></div>
1https://developer.mozilla.org/en-US/docs/Web/API/WindowOrWorkerGlobalScope/atob

It's because it can't decode the string "hello", try an actual string that can be decoded from base64, here is an example;
var tempvar = "aHR0cDovL3N0YWNrb3ZlcmZsb3cuY29tL3F1ZXN0aW9ucy80MzEyOTEzNi9kZWNvZGluZy1ub3Qtd29ya2luZy13aXRoLWJhc2U2NA==";
document.write(atob(tempvar));
If you want to encode, use the btoa function instead,
var tempvar = "hello";
document.write(btoa(tempvar));
You can use this website to test decoding and encoding base64, https://www.base64encode.org/

it's because you are trying to decode a not base64 encoded string
that it works on hi is just a coincidence it seems.
atob = decode
btoa = encode

You're using the wrong function. You should use btoa() to encode.
When you do atob('hi'), you're actually decoding 'hi', which happens to be valid base-64.

Javascript convert windows-1252 encoding to UTF-8

How do I convert the below string:
var string = "Bouchard+P%E8re+et+Fils"
using javascript into UTF-8, so that %E8 would become %C3%A8?
Reason is this character seems to be tripping up decodeURIComponent
You can test it out by dropping the string into http://meyerweb.com/eric/tools/dencoder/ and seeing the console error that says Uncaught URIError: URI malformed
I'm looking specifically for something that can decode an entire html document, that claims to be windows-1252 encoded which is where I assume this %E8 character is coming from, into UTF-8.
Thanks!

First create a map of Windows-1252. You can find references to the encoding using your search engine of choice.
For the sake of this example, I'm going to include on the character in your sample data.
Then find all the percentage signs followed by two hexadecimal characters, convert them to numbers, and convert them using the map (to get raw data), then convert them again using encodeURIComponent (to get the encoded data).
var string = "Bouchard+P%E8re+et+Fils"
var w2512chars = [];
w2512chars[232] = "è"
var percent_encoded = /(%[a-fA-F0-9]{2})/g;
function filter(match, group) {
var number = parseInt(group.substr(1), 16);
var character = w2512chars[number];
return encodeURIComponent(character);
}
string = string.replace(percent_encoded, filter);
alert(string);

Convert string to whitespace

I'm looking for av way to convert a string into whitespace; spaces, newlines and tabs, and the other way around.
I found a Python script, but I have no idea how to do it using Javascript.
I need it for a white-hacking contest.

I can has banana? ;)
var ws={x:'0123',y:' \t\r\n',a:/[\w\W]/g,b:/[\w\W]{8}/g,c:function(z){return(
ws.y+ws.x)[(ws.x+ws.y).indexOf(z)]},e:function(s){return(65536+s.charCodeAt(0)
).toString(4).substr(1).replace(ws.a,ws.c)},d:function(s){return String.
fromCharCode(parseInt(s.replace(ws.a,ws.c),4))},encode:function(s){return s.
replace(ws.a,ws.e)},decode:function(s){return s.replace(ws.b,ws.d)}};
// test string
var s1 = 'test0123456789AZaz€åäöÅÄÖ';
// show test string
alert(s1);
// encode test string
var code = ws.encode(s1);
// show encoded string
alert('"'+code+'"');
// decode string
var s2 = ws.decode(code);
// show decoded string
alert(s2);
// verify that the strings are completely identical
alert(s1 === s2);