snake game (javascript, canvas, setInterval)

snake.html

<canvas id="gc" height="600" width="600" style="margin:auto; display: block;"></canvas>
<script type="text/javascript">
window.onload = function() {
	canvas = document.getElementById('gc');
	context = canvas.getContext('2d');
	document.addEventListener('keydown', keyPush);
	setInterval(game, 40);
}

let	movX = 0;
let movY = 0;
let	prizeX = prizeY = 30;
let	headX = headY = 15;
const side = 40;
const cell = 15;
let	sElements = [];
let	sTail = 6;
let color = "blue";

function game() {

	headX += movX;
	headY += movY;

	if(headX > side-1) {
		headX = 0;
	}
	if(headX < 0) {
		headX = side-1;
	}
	if(headY > side-1) {
		headY = 0;
	}
	if(headY < 0) {
		headY = side-1;
	}

	context.fillStyle="black";
	context.fillRect(0,0,canvas.height,canvas.width);

	context.fillStyle="white";
	context.fillRect(3,3,canvas.height-6,canvas.width-6);

	for (let i = 0; i < sElements.length; i++){
		context.fillStyle=sElements[i].c;
		context.fillRect(sElements[i].x*cell,sElements[i].y*cell,cell-2,cell-2);
		if (sElements[i].x == headX && sElements[i].y == headY &&
		    (movX != 0 || movY != 0)) {
			color = getRandomRgb();
			sTail = 6;
		}
	}

	sElements.push({x:headX,y:headY,c:color});
	while(sElements.length > sTail){
		sElements.shift();
	}

	if(headX == prizeX && headY == prizeY){
		prizeX = Math.floor(Math.random() * side);
		prizeY = Math.floor(Math.random() * side);
		sTail++;
	}

	context.fillStyle="darkorange";
	context.fillRect(prizeX*cell,prizeY*cell,cell-2,cell-2);

}

function getRandomRgb() {
    let num = Math.round(0xcccccc * Math.random());
    let r = num >> 16;
    let g = num >> 8 & 255;
    let b = num & 255;
    return 'rgb(' + r + ', ' + g + ', ' + b + ')';
}

function keyPush(event) {
	switch(event.keyCode) {
		case 37:
			if(movX!=1)
				movX=-1; movY=0;
			break;
		case 38:
			if(movY!=1)
				movX=0; movY=-1;
			break;
		case 39:
			if(movX!=-1)
			movX=1; movY=0;
			break;
		case 40:
			if(movY!=-1)
			movX=0; movY=1;
			break;
		case 32:
			movX=0; movY=0;
			break;
	}
}

</script>