HTML5 Canvas driving

<canvas></canvas>

* {
   padding: 0;
   margin: 0;
}
html, body, canvas {
   position: fixed;
   width: 100%;
   height: 100%;
}

const ctx = document.querySelector("canvas").getContext("2d");

window.onload = function () {
    try {
        ctx.W = document.documentElement.clientWidth;
        ctx.H = document.documentElement.clientHeight;
        ctx.keyState = {};
        ctx.keys = {
            LEFT: 37,
            UP: 38,
            RIGHT: 39,
            DOWN: 40,
            SPACE: 32,
        };
        ctx.frameCount = 0;
        ctx.mouseX = 0;
        ctx.mouseY = 0;
        ctx.mouseDown = false;

        ctx.randomNumber = function (min, max) {
            return Math.random() * (max - min) + min;
        };

        ctx.frame = function () {
            window.requestAnimationFrame(ctx.frame);
            ctx.fit();
            ctx.clearRect(0, 0, ctx.W, ctx.H);
            ctx.screen.update();
            ctx.screen.render();
            ctx.frameCount++;
        };

        ctx.fit = function () {
            ctx.W = document.documentElement.clientWidth;
            ctx.H = document.documentElement.clientHeight;
            ctx.canvas.width = ctx.W;
            ctx.canvas.height = ctx.H;
        };

        ctx.input = function () {
            document.body.onmousedown = function () {
                ctx.mouseDown = true;
            };

            document.body.onmouseup = function () {
                ctx.mouseDown = false;
            };

            document.body.ontouchstart = function () {
                ctx.mouseDown = true;
            };

            document.body.ontouchend = function () {
                ctx.mouseDown = true;
            };

            document.body.onmousemove = function (e) {
                ctx.mouseX = e.clientX;
                ctx.mouseY = e.clientY;
            };

            document.body.onkeydown = function (e) {
                ctx.keyState[e.keyCode] = true;
            };

            document.body.onkeyup = function (e) {
                delete ctx.keyState[e.keyCode];
            };
        };

        ctx.screen = new Screen();

        ctx.input();
        ctx.fit();
        ctx.frame();
    } catch (error) {
        console.error(error);
        console.error("Please provide a Screen constructor");
    }
};

function Screen() {
    this.circle = {
        x: ctx.W / 2,
        y: ctx.H / 2,
        r: 40,
    };
    this.wheel = {
        x: 0,
        y: 0,
        r: 10,
    };

    this.xv = 1.1;
    this.yv = 1.1;

    this.angle = 0;
    this.speed = 0.05;
}

Screen.prototype.render = function () {
    ctx.fillStyle = "#555555";
    ctx.fillRect(0, 0, ctx.W, ctx.H);

    ctx.beginPath();
    ctx.strokeStyle = "#ffffff";
    ctx.arc(this.circle.x, this.circle.y, this.circle.r, 0, Math.PI * 2);
    ctx.stroke();

    ctx.beginPath();
    ctx.fillStyle = "#ffffff";
    ctx.arc(this.wheel.x, this.wheel.y, this.wheel.r, 0, Math.PI * 2);
    ctx.fill();
};

Screen.prototype.update = function () {
    this.wheel.x = this.circle.x + this.circle.r * Math.cos(this.angle);
    this.wheel.y = this.circle.y + this.circle.r * Math.sin(this.angle);
    if (ctx.keyState[ctx.keys.LEFT]) {
        this.angle -= this.speed;
    }
    if (ctx.keyState[ctx.keys.RIGHT]) {
        this.angle += this.speed;
    }

    if (ctx.keyState[ctx.keys.UP]) {
        this.circle.x += this.xv * Math.cos(this.angle);
        this.circle.y += this.yv * Math.sin(this.angle);
    }

    if (ctx.keyState[ctx.keys.DOWN]) {
        this.circle.x -= this.xv * Math.cos(this.angle);
        this.circle.y -= this.yv * Math.sin(this.angle);
    }
};