A Randomized Game

At the end of lesson 4 we get to build a small "dragon slaying" game. It also expands a little on the Math.random() command we learned about earlier (coin toss game).

I'm going to the experts on this. Mozilla explains Math.floor() like this:

The Math.floor() function returns the largest integer less than or equal to a given number.

Here's a sample of what Math.floor() would do with some numbers (the opposite of Math.floor() is Math.ceil(), there's also Math.round() which does traditional rounding.):

Original Math.floor()
1.47 1
61.9 61
-1.3 -2
0.3 0

Here's the little game. I'll break it down below:

var slaying = true;
var youHit = Math.floor(Math.random()*2);
var damageThisRound = Math.floor(Math.random()*2 + 1);
var totalDamage = 0;

while(slaying) {
    if (youHit) {
        console.log("Woohoo! You got him!");
        totalDamage += damageThisRound;
        if (totalDamage >= 4) {
            console.log("Dude's dead! You are the winner!");
            slaying = false;
        else {
            youHit = Math.floor(Math.random()*2);
    else {
        console.log("You suck! Get a job!");
        slaying = false;
  • Math.floor(Math.random()*2)
    • The first thing we do is Math.random() which gives us a number between 0 and 1. So 0.34 or 0.71 for example.
    • We want to be able to get either 0 or 1 specifically, so we need to do some rounding. That's what Math.floor() is for. Look, a rhyme. The problem is both 0.34 and 0.71 will become 0 using Math.floor().
    • We take our random numbers and multiply them by 2, making them 0.68 and 1.42. Now Math.floor() will turn them into 0 and 1. Problem solved.
    • I'm not sure why we don't just use Math.round(), I'm pretty sure that would work just the same. Maybe it's not as fair in the case of 0.5?
  • Settings up the variables
    1. The first variable is slaying. If it's true we're still trying to slay the dragon. If it's false we've stopped.
    2. youHit determines whether or not you were able to hit the dragon. It will be either 0 or 1 based on Math.floor(Math.random() * 2);
    3. Our next variable, damageThisRound, decides how much damage we do. We can get 1 or 2 points. (See youHit).
    4. Our final variable is totalDamage which is used to keep the score.
  • Step by Step
    1. We create an if statement that's true while youHit is 1 - if (youHit)
    2. When we first run this code youHit gets assigned a random value - var youHit = Math.floor(Math.random()*2);. If the initial value is 1, it continues into the second if/else (if (totalDamage >= 4)) inside the first if, otherwise it drops down to the first else (console.log("You suck! Get a job!");, in which case the game is over.
    3. Next up we add the value of this round's damage to the total damage, introducing some new syntax (is this plus that) : totalDamage += damageThisRound;.
    4. Now we test the second if where the total damage must be equal to or larger than 4 for us to win. This can only happen after at least 2 hits with a damageThisRound of 2.
    5. If our totalDamage is not >= 4 the else runs and assigns a new random number to youHit. We're sent back to the first if to see if we get another try, or if the dragon killed us.
    6. This keeps on happening until damageThisRound >= 4 and we win, or until youHit = 0 and we lose.