JS Web Audio API Gain Volume SRC

<script>
var audioCtx=new AudioContext();
var oscillator = audioCtx.createOscillator();
var gainNode = audioCtx.createGain();
oscillator.connect(gainNode);
gainNode.connect(audioCtx.destination);
var Outt=prompt('Enter Value (0.1 to 1.0:)');
var WIDTH = window.innerWidth;
var HEIGHT = window.innerHeight;
var FreqMax = 200;
var VolMax = 1.0;
var Freq = 50;
var Vol = Outt;
gainNode.gain.value=parseFloat(Outt);
oscillator.type = 'sawtooth';
oscillator.frequency.value = Freq;oscillator.start();
</script>

<button onclick="gainNode.gain.value=0.0;">0.0</button>

<button onclick="gainNode.gain.value=0.1;">0.1</button>

<button onclick="gainNode.gain.value=0.2;">0.2</button>

<button onclick="gainNode.gain.value=0.3;">0.3</button>

<button onclick="gainNode.gain.value=0.4;">0.4</button>

<button onclick="gainNode.gain.value=0.5;">0.5</button>

<button onclick="gainNode.gain.value=0.6;">0.6</button>

<button onclick="gainNode.gain.value=0.7;">0.7</button>

<button onclick="gainNode.gain.value=0.8;">0.8</button>

<button onclick="gainNode.gain.value=0.9;">0.9</button>

<button onclick="gainNode.gain.value=1.0;">1.0</button>