freefall.js

var canvas = document.getElementById('canvas');
var context = canvas.getContext('2d');

var g = 0.1;
var radius = 10;
var color;
var balls;
var numBalls = 6;

//window.onload = init; 

function init() {
    balls = new Array();
    for (var i = 0; i < numBalls; i++) {
        var ball = new Ball(Math.random() * 25, getRandomColor());
        ball.x = Math.random() * 300; //x axis positions are random
        ball.y = 0;
        ball.vx = 0;
        ball.vy = 0;
        ball.draw(context);
        balls.push(ball);
    }
    setInterval(onEachStep, 1000 / 60); // 60 fps
}

function onEachStep() {
    context.clearRect(0, 0, canvas.width, canvas.height);
    for (var i = 0; i < numBalls; i++) {
        var ball = balls[i];
        ball.vy += g;

        ball.x += ball.vx;
        ball.y += ball.vy;

        if (ball.y > canvas.height - radius) {
            ball.y = canvas.height - radius;
            ball.vy *= -0.3;
        }
        if (ball.x > canvas.width + radius) {
            ball.x = -radius;
        }
        ball.draw(context);
    }
}

//random color function
function getRandomColor() {
    var letters = '0123456789ABCDEF';
    var color = '#';
    for (var i = 0; i < 6; i++) {
        color += letters[Math.floor(Math.random() * 16)];
    }
    return color;
}