Solve the Trello dev challenge (https://trello.com/jobs/developer) recursively using ES6 features.

my_es6_trello_dev_challenge.js

function unhash(hash, str="") { //default parameter values currently only supported by Firefox 
    var base = 7;
    var multiplier = 37;
    var letters = "acdegilmnoprstuw";
    var index = hash % multiplier;
    str = letters[index] + str;
    hash = Math.trunc(hash / multiplier);
    //Math.trunc is a dumb Math.floor - splits by the decimal point
    //so works for negative numbers also 
    //(obviously doesn't make a difference here, 
    //but it's recommended over Math.floor to get the quotient)
    if (hash === base)
    	return str
    return unhash(hash, str)
}
unhash(956446786872726) === "trellises"

transpiled_es5_trello_dev_challenge.js

//this is how babel transpiled the code to ES5 - wow
function unhash(_x2) {
    var _arguments = arguments;
    _function: while (true) {
        var hash = _x2;
        str = base = multiplier = letters = index = undefined;
        var str = _arguments[1] === undefined ? "" : _arguments[1];
        //default parameter values currently only supported by Firefox
        var base = 7;
        var multiplier = 37;
        var letters = "acdegilmnoprstuw";
        var index = hash % multiplier;
        str = letters[index] + str;
        hash = Math.trunc(hash / multiplier);
        //Math.trunc is a dumb Math.floor - splits by the decimal point
        //so works for negative numbers also
        //(obviously doesn't make a difference here,
        //but it's recommended over Math.floor to get the quotient)
        if (hash === base) {
            return str;
        }_arguments = [_x2 = hash, str];
        continue _function;
    }
}
unhash(956446786872726) === "trellises";