通过单选按钮的值控制文本区域的元素属性

<form>
  <input type="radio" name="attribute" value="bold"> 加粗
  <input type="radio" name="attribute" value="italic"> 斜体
  <input type="radio" name="attribute" value="underline"> 下划线
  <br>
  <textarea id="textArea"></textarea>
</form>

var radios = document.getElementsByName('attribute');
var textArea = document.getElementById('textArea');

for (var i = 0; i < radios.length; i++) {
  radios[i].addEventListener('change', function() {
    if (this.value === 'bold') {
      textArea.style.fontWeight = 'bold';
    } else if (this.value === 'italic') {
      textArea.style.fontStyle = 'italic';
    } else if (this.value === 'underline') {
      textArea.style.textDecoration = 'underline';
    }
  });
}