html:

<ul>
        <li>1</li>
        <li>1</li>
        <li id="one">1</li>
        <li>1</li>
        <li>1</li>
        <li>1</li>
        <li>1</li>
        <li>1</li>
        <li>1</li>
        <li>1</li>
        <li>1</li>
        <li>1</li>

js:

  var oli= document.getElementById("one");;
    oli.style.color = "red";
    function siblings(item) {
        var p = item.parentNode.children;//获取父级所有子集元素
           for (var i = 0, pl = p.length; i < pl; i++) {
        if (p[i] !== item) {           //删除自己
        p[i].style.color = "gray"; //执行事件
        }
    }
    }
        siblings(oli);