启用语音识别时如何禁止number输入框显示文本？

HTML #

<form action="">
  <label for="quantity">Quantity (between 1 and 5):</label>
  <input type="number" id="quantity" name="quantity" min="1" max="5">
  <input type="submit">
</form>

CSS #

[type="number"]{
  width:200px;
  height:40px;
}

JavaScript #

document.querySelector('#quantity').webkitSpeech = false;

内容的提问来源于stack exchange，提问作者Hardik Godhani