JavaScript: "Math.floor" & "Math.random" & "function" & "if / else"

I started to learn programming just a few days ago. And I've written code for a simple original game for practice, using the knowledge of JavaScript that I have gained so far.

Is the following code properly written? I'm especially concerned about the use of "Math.floor", "Math.random", "function", and "if / else".

Incidentally, "Metal King" is the name of a monster in the game, and "Angelo" is a character.

alert("Metal Kings (A, B, and C) have appeared!");



// Which Metal King (A, B, or C) will Angelo decide to attack? \
// 33% probability for each.

var MetalKingABC = 1 + Math.floor(Math.random() * 3);


if (MetalKingABC === 1) {
    MetalKingABC = "Metal King A";
}
else if (MetalKingABC === 2) {
    MetalKingABC = "Metal King B";
}
else {
    MetalKingABC = "Metal King C";
}



var WhichOneToAttack = function(MonsterName) {

    alert("Angelo is about to attack " + MonsterName + ".");


    // Metal King has a 50% chance of fleeing the battle.

    var FleeOrFight = 1 + Math.floor(Math.random() * 2);


    if (FleeOrFight === 1) {
        alert(MonsterName + " flees like lightning!");
        // The battle ends here before Angelo attacks.
    }

    else // Metal King stays, and Angelo attacks.
    {
        // 70% chance of MISS, 20% of ONE damage, 10% of Critical.

        var MissOneCritical = 1 + Math.floor(Math.random() * 10);

        if (MissOneCritical <= 7) {
            alert(MonsterName + " swiftly evades Angelo's attack.");
        }

        else if (MissOneCritical <= 9) {
            alert("Angelo inflicts 1 point of damage on " + MonsterName + ".");
        }

        else {
            // The damage dealt by a critical hit can range from 197 to 256 points.

            var CriticalRange = 197 + Math.floor(Math.random() * 60);

            alert("Angelo lands a critical hit on " + MonsterName + ", dealing massive \
            damage of " + CriticalRange + " points! Angelo defeats " + MonsterName + ".");

            // When defeated, Metal King drops a shield with an 80% probability.

            var ShieldDrop = 1 + Math.floor(Math.random() * 10);

            if (ShieldDrop <= 8) {
                alert(MonsterName + " drops a shield. Angelo obtains a Diamond Shield!");                
            }
            else {
            // No code is written in this else portion, since Metal King didn't drop \
            // any item.  
            }
        }
    }
};

// Finally, call the function.

WhichOneToAttack(MetalKingABC);