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    <input type="text" id="txt" placeholder="輸入要添加的文本" />
    <button id="btn">加 </button>
    <ul id="ul">
        <li>11111</li>
        <li>22</li>
        <li>3333</li>
        <li>4444</li>
    </ul>
    <script type="text/javascript">
        var ul = document.getElementById("ul");
        var lis = ul.getElementsByTagName('li');
        var btn = document.getElementById("btn");
        
        btn.onclick = function() {   //動態(tài)添加li
            var txt = document.getElementById("txt"),
                txtValue = txt.value,
                ali = document.createElement("li");
                console.log(txt.value);                    
                ali.innerHTML = txtValue;
                ul.appendChild(ali);
        }
        
        ul.onmouseover = function(ev) {
            var ev = ev || window.event;   //獲取發(fā)生事件 event 兼容      =====1
            var target = ev.target || ev.srcElement;   //獲取真正被觸發(fā)的元素     =====2
            if (target.nodeName.toLocaleLowerCase() == 'li') {
                //判斷target是否是所需要的元素  正是因為這個判斷 我們可以得到任何想要的元素  a li td 等等
                target.style.background = "red";
            }
        }
        ul.onmouseout = function(ev) {
            var ev = ev || window.event;
            var target = ev.target || ev.srcElement;
            if (target.nodeName.toLocaleLowerCase() == 'li') {
                target.style.background = "";
            }
        }
    </script>

標註的1和2兩處的程式碼的寫法怎麼理解？看不懂= =哪來的api