playing around a joke sequence

seq.js

var next = (numberString) =>{
    const count = [0, 0, 0, 0, 0, 0, 0, 0, 0, 0]
    for(c of numberString){
        count[parseInt(c)]++
    }
    let nextString = ""
    for(c of numberString){
        if(count[parseInt(c)] > 0){
            nextString += count[parseInt(c)] + c
            count[parseInt(c)] = 0
        }
    }
    
    return nextString
}

var printSeq = (start) => {
    let previous = start

    console.log(previous)
    const alreadyCounter = new Set()
    while(!alreadyCounter.has(previous)){
        alreadyCounter.add(previous)
        previous = next(previous)
        console.log(previous)
    }
    console.log(previous)
    console.log("loop "+ alreadyCounter.size)
}

var convergence = (start) => {
    let previous = start + ""
    let count = 0
    const alreadyCounter = new Set()
    while(!alreadyCounter.has(previous)){
        alreadyCounter.add(previous)
        previous = next(previous)
        count++
    }
    return [previous, count]
}

var stableIslands = new Set()
for(let i=0; i<=100000; i++){
    let conv = convergence(i)
    str = conv[0].substring(0, conv[0].length - 1)
//     stableIslands.add(str + "X")
    stableIslands.add(conv[0])

    //console.log(i+" times:"+conv[1]+": "+conv[0])
}
console.log(stableIslands)