JSFiddle - React, Tailwind, and code Playground

HTML

<input type="range" min="0" max="1000" id="fm" value="0" /> More FM!
<br/>
<input type="range" min="1" max="600" id="lfo" value="300" /> LFO Frequency

JavaScript

var context = new webkitAudioContext();
var osc = context.createOscillator();
var lfo = context.createOscillator();
var lfoGain = context.createGain();
var oscGain = context.createGain();

lfo.frequency.value = 300;
lfo.type = 0; // sinus
lfoGain.gain.value = 0;
lfo.connect(lfoGain);
lfoGain.connect(osc.frequency);

osc.frequency.value = 300;
osc.type = 0; // sinus
oscGain.gain.value = 1;
osc.connect(oscGain);
oscGain.connect(context.destination);

osc.start(0);
lfo.start(0);


var fmSlider = document.getElementById("lfo");
fmSlider.addEventListener('change', function() {
	lfo.frequency.value = fmSlider.value;
});  

var lfoSlider = document.getElementById("fm");
lfoSlider.addEventListener('change', function() {
	lfoGain.gain.value = lfoSlider.value;
});