ds.js

function d(n) {
    return Math.floor(Math.random() * n) + 1;
}

function attack(attacker, enemy) {
    var a = d(20), p = d(20);
    if (a <= attacker.at) {
        if (a === 1) a = attack.at;
        if (p <= enemy.pa) {
            if (p === 1) p = enemy.pa;
            a -= p;
        }
        if (a > 0) {
            enemy.lp -= a;
            return enemy.lp <= 0;
        }
    }
    return false;
}

function turnsToKillAlric() {
    var alrik = {
        lp: 21,
        at: 13,
        pa: 13
    };
    for (var turn = 1; ; turn++) {
        if (attack(alrik, alrik)) {
            return turn;
        }
    }
}

var turns = 0, count = 10000;
for (var i = 0; i < count; i++) {
    turns += turnsToKillAlric();
}

console.log(turns / count);

dsa1.js

function d(n) {
    return Math.floor(Math.random() * n) + 1;
}

function attack(attacker, enemy) {
    if (d(20) <= attacker.at) {
        if (!(d(20) <= enemy.pa)) {
            enemy.lp -= Math.max(attacker.weapon() - enemy.rs, 0);
            return enemy.lp <= 0;
        }
    }
    return false;
}

function sword() {
    return d(6) + 4;
}

function turnsToKillAlric() {
    var alrik = {
        lp: 30,
        at: 10,
        pa: 4,
        rs: 3,
        weapon: sword
    };
    for (var turn = 1; ; turn++) {
        if (attack(alrik, alrik)) {
            return turn;
        }
    }
}

var turns = 0, count = 10000;
for (var i = 0; i < count; i++) {
    turns += turnsToKillAlric();
}

console.log(turns / count);