game calculator

<script type="text/javascript">
function w(message) {
    console.log(message);
}

function Skill(name, damage, frequency, initialCooldown) {
    this.name = name;
    this.damage = damage;
    this.frequency = frequency; // how often this skill is used
    this.cooldown = initialCooldown || 0; // the time when this skill will be ready to be used/reused
    this.used = 0; // the time when this skill was last used
}

Skill.prototype.toString = function() {
    return this.name + " " + this.damage + "/" + this.frequency;
};

Skill.prototype.use = function() {
    this.used = this.cooldown;
    this.cooldown += this.frequency;
};

function Champion(name, hp, startCooldownOn, doListener) {
    this.name = name;
    this.hp = hp;
    this.skills = [];
    this.doListener = doListener || function(){};
}

Champion.prototype.installSkill = function(skill) {
    this.skills.push(skill);
};

Champion.prototype.getShortestCooldownSkill = function() {
    if(this.skills.length === 0)
        w("No skill has been installed.");

    var shortestCooldownSkill = this.skills[0];
    this.skills.forEach(function(skill) {
        if(skill.cooldown < shortestCooldownSkill.cooldown)
            shortestCooldownSkill = skill;
    }.bind(this));
    return shortestCooldownSkill;
};

Champion.prototype.do = function() {
    var skills = [];
    do {
        var skill = this.getShortestCooldownSkill()
        skill.use();
        skills.push(skill);
        /*
         * Is the time when the skill was last used the same as when the next
         * skill will be ready? Then they're being called at the same time
         */
    } while(skill.used === this.getShortestCooldownSkill().cooldown);
    // calls the listener passing all the skills that are being called at this instant
    this.doListener(skills);
    return skill;
};

Champion.prototype.addDoListener = function(doListener) {
    this.doListener = doListener;
};

function doListener(skills) {
    var text = "";
    var damage = 0;
    var time = skills[0].used + "s";
    var tr = document.createElement("tr");
    // create and set this static variable to 0 if it hasn't been created yet
    doListener.totalDamage = doListener.totalDamage || 0;

    skills.forEach(function(skill) {
        text += skill.toString() + "<br>";
        damage += skill.damage;
    });
    doListener.totalDamage += damage;

    tr.innerHTML = "<td>" + time + "</td><td>" + text + "</td><td>" + damage + "</td>";
    document.getElementById("battleLog").getElementsByTagName("tbody")[0].appendChild(tr);
    document.getElementById("totalDamage").innerHTML = doListener.totalDamage;
    document.getElementById("totalTime").innerHTML = time;
}

var Ashe = new Champion("Alistar", 1000);
Ashe.addDoListener(doListener);
Ashe.installSkill(new Skill("Dashing Hoof", 50, 2));
Ashe.installSkill(new Skill("Metal Horn", 30, 1));
Ashe.installSkill(new Skill("Burning Milk", 5, 0.5));
</script>
<style type="text/css">
    table {border: 1px solid black;}
    td {border:1px solid black;text-align:center;padding:2px 30px;}
    tbody tr:nth-child(odd) {background-color:#eee;}
    tfoot {font-weight:bold;background-color:#aaa;}

</style>
<input type="button" value="Atacar" id="atacar" onclick="Ashe.do()" />
<table id="battleLog">
    <thead>
        <tr>
            <th>Time</th>
            <th>Skill(s)' Names Damage / Frequency</th>
            <th>Damage</th>
        </tr>
    </thead>
    <tfoot>
        <tr>
            <td id="totalTime"></td>
            <td></td>
            <td id="totalDamage"></td>
        </tr>
    </tfoot>
    <tbody>
    </tbody>
</table>