<label id="myLabel" for="male">Male</label>
<input type="radio" name="sex" id="male" value="male"><br>
<p>点击按钮来获得 label 所绑定元素的 id。</p>
<button onclick="myFunction()">试一下</button>
var x = document.getElementById("myLabel").htmlFor;
document.getElementById("demo").innerHTML = x;