let direction = 'left';
let invaders = document.getElementById("invaders");
let i = 0;
function move() {
if(i > 677) {
	direction = 'right'
}

else if (i < 5){
	direction = 'left'
}

if(direction == 'left'){
	invaders.style.left = i + 'px';
	i++;
}

else if(direction == 'right'){
	invaders.style.left = i + 'px';
	i--;
}

}
window.onload = setInterval(move, 10)