RLE

"use strict"
test();

function test() {
    let test1 = "aaaaaabccccceekkk";
    let test2 = "aaaa$$$$bcce$ekkkk";
    let test1Encoded = Encode(test1);
    let test2Encoded = Encode(test2);
    let test1Decoded = Decode(test1Encoded);
    let test2Decoded = Decode(test2Encoded);
    console.log(test1 == test1Decoded);
    console.log(test2 == test2Decoded);
}

function Encode(message) {
    result = ""
    let sequenceLength = 1;
    for (let i = 1; i < message.length + 1; i++) {
        if (message[i] == message[i - 1]) {
            sequenceLength++;
        } else {
            if (sequenceLength > 3 || IsSpecialSymbol(message[i - 1])) {
                result += GetEncodedSequence(message, sequenceLength, i - 1);
            } else {
                result += GetNotEncodedSequence(message, sequenceLength, i - 1);
            }
            sequenceLength = 1;
        }
    }
    return result;
}


function Decode(message) {
    result = "";
    let i = 0;
    while (i < message.length) {
        if (IsSpecialSymbol(message[i])) {
            result += GetDecodedSequence(message.charCodeAt(i + 1), message[i + 2]);
            i += 3;
        } else {
            result += message[i];
            i++;
        }
    }
    return result;
}


function GetDecodedSequence(sequenceLength, symbol) {
    result = "";
    for (let i = 0; i < sequenceLength; i++) {
        result += symbol;
    }
    return result;
}

function GetNotEncodedSequence(message, sequenceLength, lastSymbolPosition) {
    return message.slice(lastSymbolPosition - sequenceLength + 1, lastSymbolPosition + 1);
}

function GetEncodedSequence(message, sequenceLength, lastSymbolPosition) {
    return String.fromCharCode(36) + String.fromCharCode(sequenceLength) + message[lastSymbolPosition];
}

function IsSpecialSymbol(symbol) {
    return symbol == String.fromCharCode(36);
}