Hide text in string using unicode

encode.js

/* Code from https://syllab.fr/projets/experiments/wutf/ */

var placeholders = [
    "Hey ! What's up ?",
    "Hello !?",
    "Yop !",
    "You're here ?",
    "Got a second ?",
    "I need you man",
    "Plans for the week end ?",
    "This movie is so bad",
    "I ate too much candies",
    "I am sick",
    "I am soo exhausted...",
    "please ?",
    "what ?",
    "Did you see Jim ?",
    "How are you ?",
    "I go to sleep",
    "brb",
    "Come on !",
    "it's raining cows today",
    "man its so hot",
    "brrrr so cold",
    "I bought a new phone",
    "Give me a break !",
    "can't tell",
    "i don't know sorry",
    "yes of course !",
    "nope",
    "yeah sure",
    "no never",
    "hey yo",
    "call me when you got this",
    "where are u",
    "bar at 7 ?",
    "did you see my phone ?",
    "happy birthday !",
];

var charToHex = function (c) { return c.charCodeAt(0).toString(16); };
var SERROGATE_PAIR = "%uDB40";

var convertChar = function (c) { return SERROGATE_PAIR + "%uDD" + charToHex(c).slice(0, 2); };
var randomPlaceholder = function () { return placeholders[Math.floor(Math.random() * placeholders.length)]; };

function encode(s, placeholder) {
    //s = s.normalize('NFD').replace(/[\u0300-\u036f]/g, "")  // remove diactrics
    var chars = s.split('');
    if (!placeholder || placeholder.length < 2)
        placeholder = randomPlaceholder();
    return unescape(placeholder[0] + chars.map(convertChar).join('') + placeholder.substr(1));
}

function decode(s) {
    var escaped = escape(s);
    if (!escaped.includes(SERROGATE_PAIR))
        return "(this text does not seem to be encoded)";
    var lastSecretChar = escaped.lastIndexOf(SERROGATE_PAIR) + 2 * SERROGATE_PAIR.length;
    return unescape(escaped.substring(1, lastSecretChar).replace(/u.{8}/g, ''));
}

https://freetools.textmagic.com/unicode-detector
https://www.soscisurvey.de/tools/view-chars.php