Help - Anfängerfehler?

Code:
<!DOCTYPE html>

<html lang='en'>



<head>

    <meta charset='UTF-8'>

    <meta name='viewport' content='width=device-width, initial-scale=1.0'>

    <title>Galaxy War</title>



<style>

    canvas {

      background-color: rgba(0, 0, 0, 0.8);

    }

</style>



<script>

let KEY_SPACE = false;// 32

let KEY_UP = false;// 38

let KEY_DOWN = false;// 40

let canvas;

let ctx;

let backgroundImage = new Image();



let rocket = {

    x: 100,

    y: 200,

    width: 200,

    height: 80,

    src: 'img/rocket.png'

}



let ufo = {

    x: 500,

    y: 200,

    width: 100,

    height: 40,

    src: 'img/ufo.png'

}









document.onkeydown = function(e) {

    if (e.keyCode == 32) // Leertaste gedrückt

    KEY_SPACE = true;





if (e.keyCode == 38) // Nach oben gedrückt

KEY_UP = true;





if (e.keyCode == 40) // Nach unten gedrückt

KEY_DOWN = true;

}



document.onkeyup = function(e) {

    console.log(e.keycode);

    if (e.keycode == 32) // Leertaste losgelassen

    KEY_SPACE = false;





if (e.keycode == 38) // Nach oben losgelassen

KEY_UP = false;





if (e.keycode == 40) // Nach unten losgelassen

KEY_DOWN = false;

}











function startGame(){

    canvas = document.getElementById("canvas");

    ctx = canvas.getContext('2d');

    loadImages();

    update();

    draw();

    //.calculate





}



function loadImages(){

    backgroundImage.src = 'img/background.png';

    rocket.img = new Image();

    rocket.img.scr = rocket.scr;



    ufo.img = new Image();

    ufo.img.scr = ufo.scr;





}





function draw(){

    ctx.drawImage(backgroundImage, 0, 0);

    ctx.drawImage(rocket.img, rocket.x, rocket.y, rocket.width, rocket.height);













    requestAnimationFrame(draw);

}

</script>



</head>



<body onload='startGame'()>

   <canvas id='canvas' width='720' height='480'></canvas>



</body>



</html>