This should do it.

function _getMicrophoneUserMedia() {
  if (!navigator.mediaDevices) navigator.mediaDevices = 
    navigator.webkitMediaDevices || navigator.mozMediaDevices || 
    navigator.msMediaDevices;
  if (!navigator.mediaDevices) throw Error('Browser does not support mediaDevices.');
  return navigator.mediaDevices.getUserMedia({
    video: false,
      audio: {
      echoCancellation: true,
      noiseSuppression: true,
    },
  });
}

function _getBestBufferSize() { // Return 0 unless it's on a browser that has problems in their implementation.
  return typeof window.AudioContext === "undefined" ? 4096 : 0;
}

async function startRecording(audioContext, onReceiveAudio) {
  const mediaStream = await _getMicrophoneUserMedia();
  const bufferSize = _getBestBufferSize();

  const inputChannels = 1; // Nearly every mic will be one channel.
  const outputChannels = 1; // Chrome is buggy and won't work without this.

  // createScriptProcessor() is deprecated, but the AudioWorklet 
  // solution is more complicated and won't work in Webpack without 
  // configuration of loaders.
  const recorder = context.createScriptProcessor(
    bufferSize, inputChannels, outputChannels
  );

  recorder.connect(context.destination);
  const audioInput = context.createMediaStreamSource(mediaStream);
  audioInput.connect(recorder);

  recorder.onaudioprocess = (e) => {
    const samples = e.inputBuffer.getChannelData(0);
    if (!samples.length) return;
    onReceiveBuffer(e.inputBuffer);
  };
}

// Start recording - onReceiveAudio is a callback you've defined.
const audioContext = new AudioContext(); // It's good to pool and reuse.
startRecording(audioContext, onReceiveAudio);