var oBtn12_1=document.getElementById('btn12_1');
    var oUl12_1=document.getElementById('ul12_1');
    var oTxt12_1=document.getElementById('text12_1');
    
    oBtn12_1.onclick=function()
    {
        var oLi12_1=document.createElement('li');//creatElement（'需要创造的标签'）
        oLi12_1.innerHTML=oTxt12_1.value; 
        oTxt12_1.value=''; 
        oUl12_1.appendChild(oLi12_1);	//父级.appendChild(子节点); 添加到末尾
    }