function stringZip(iStr) {
    var res = "";
    var temp = 1;
    for (var i = 0, len = iStr.length; i < len; i++) {
        if (i === 0) {
            res = len===1? "1" + iStr[i] : ""
        } else if (iStr[i] === iStr[i-1]) {
            temp++
        } else {
            res += temp + iStr[i-1]
            temp = 1
        }
        if(i >= len - 1 && len > 1){
            res += temp + iStr[i-1]
        }        
    }
    return res
}

function stringUnZip(iStr) {
    var str = ""
    for(var i = 0,len=iStr.length;i<len;i+=2){
        for(var j = 0; j<iStr[i];j++){
            str += iStr[i+1]
        }
    }   
    return str 
}

console.log(stringZip("aaabccccaaaaccddecccee"));
console.log(stringZip("a"));

console.log(stringUnZip("3a1b6c2d3e"));
console.log(stringUnZip("1a"));