Web Audio APIで音源ファイルを使わずにブラウザから音を出す

class WAPAudioWorklet extends AudioWorkletProcessor {
	constructor(options) {
		super();

		var WEBAUDIOAWP_internal = function (samplingRate) {
			var counter = 0;
			var toneFreqHz = 0;

			var result;
			var scale = toneFreqHz == 0 ? samplingRate / toneFreqHz : 0; // 発声する周波数と実行環境のサンプリングレートの比

			// 波形データ生成
			this.getWave = function () {
				if (toneFreqHz == 0) return 0;

				// 正弦波
				result = Math.sin(Math.PI * 2 * counter / scale);

				counter++;
				if (counter > scale) counter = 0;

				return (result); // -1 〜 +1
			};

			this.setFrequency = function (freq) {
				toneFreqHz = freq;
				counter = 0;
				scale = toneFreqHz != 0 ? samplingRate / toneFreqHz : 0;
			};

		};

		var sampleRate;
		if (options.processorOptions) {
			sampleRate = options.processorOptions.rate;
		}
		this.wap = new WEBAUDIOAWP_internal(sampleRate);
		this.enable = false;

		this.port.onmessage = (event) => {
			const message = event.data;
			switch (message.message) {
				case 'frequency':
					// 発音周波数
					this.wap.setFrequency(message.freq);
					break;
			}
		}
	}

	// AudioWorkletProcessor interface
	process(inputs, outputs, parameters) {
		if (!this.enable) {
			this.enable = true;
			this.port.postMessage({
				message: 'enabled'
			});
		}

		var output = outputs[0];
		var len = output[0] ? output[0].length : 0;

		for (var i = 0; i < len; i++) {
			const out = this.wap.getWave();
			output[0][i] = out;
		}
		return true;
	}
}
registerProcessor("WEBAUDIO", WAPAudioWorklet);