note-a.js

let playButton = document.createElement('button');
playButton.textContent = 'Play';
document.body.appendChild(playButton);

playButton.addEventListener('click', () => {
	let audioCtx = new AudioContext();
	let sampleRate = audioCtx.sampleRate;

	let totalSeconds = 2;

	let arrayBuffer = audioCtx.createBuffer(
		1,
		sampleRate * totalSeconds,
		sampleRate,
	);

	let amplitudes = arrayBuffer.getChannelData(0);

	let sinGenerator = getSin({
		sampleRate,
		frequency: 440,
	});

	for (let i = 0; i < amplitudes.length; i++) {
		amplitudes[i] = sinGenerator.next().value;
	}

	let source = audioCtx.createBufferSource();
	source.buffer = arrayBuffer;
	source.connect(audioCtx.destination);
	source.start();
});

function* getSin({ sampleRate, frequency }) {
	let i = 0;

	while (true) {
		let p = i / sampleRate;
		let s = Math.sin(p * 2 * Math.PI * frequency);

		yield s;

		i++;
	}
}