JS Cuztomizable Mouse Synth

<script>
var audioCtx=new AudioContext();
var oscillator = audioCtx.createOscillator();
var gainNode = audioCtx.createGain();
oscillator.connect(gainNode);
gainNode.connect(audioCtx.destination);
var WIDTH = window.innerWidth;
var HEIGHT = window.innerHeight;
var FreqMax = prompt('Enter Max Freq:');
var VolMax = prompt("Enter Max Vol:");
var Freq = prompt("Enter Freq");
var Vol = 0.1;
oscillator.type = 'sawtooth';
oscillator.frequency.value = Freq;
oscillator.start();
gainNode.gain.value = Vol;
var CurX;
var CurY;
document.onmousemove = updatePage;
function updatePage(e) {
CurX = (window.Event) ? e.pageX : event.clientX + (document.documentElement.scrollLeft ? document.documentElement.scrollLeft : document.body.scrollLeft);
CurY = (window.Event) ? e.pageY : event.clientY + (document.documentElement.scrollTop ? document.documentElement.scrollTop : document.body.scrollTop);
oscillator.frequency.value = (CurX/WIDTH) * FreqMax;
gainNode.gain.value = (CurY/HEIGHT) * VolMax;
canvasDraw();
}
</script>