label for input onClick发生了什么？

测试代码如下

• html

<label for="ipt" id="label_ipt">上传</label>
<br />
<input type="file" id="ipt" />

• js

window.onload = function () {
  function iptClick () {
    console.log("iptClick")
  }
  function iptClick2() {
    console.log("iptClick2")
  }
  ipt.onclick = iptClick;
  label_ipt.onclick = iptClick2;
}

• 点击label之后的打印为iptClick2, iptClick

codepen地址

thanks