js中三种弹窗
1）
alert 弹出警告 无返回值－－－－－－－－－alert('第一行\n第二行');2）
confirm()选择确定或取消，返回t或f－－－－var result = confirm('是否删除！');3）
prompt()弹出输入框，返回输入内容－－－－var value = prompt('输入你的名字：','请在这里输入名字');
//window.confirm
//prompt
window.alert = function(title,str)
{
var shield = document.createElement("DIV");
shield.id = "shield";
shield.style.position = "absolute";
shield.style.left = "0px";
shield.style.top = "0px";
shield.style.width = "100%";
shield.style.height = document.body.scrollHeight+"px";
//弹出对话框时的背景颜色
shield.style.background = "#fff";
shield.style.textAlign = "center";
shield.style.zIndex = "25";
//背景透明 IE有效
//shield.style.filter = "alpha(opacity=0)";
var alertFram = document.createElement("DIV");
alertFram.id="alertFram";
alertFram.style.position = "absolute";
alertFram.style.left = "50%";
alertFram.style.top = "50%";
alertFram.style.marginLeft = "-225px";
alertFram.style.marginTop = "-75px";
alertFram.style.width = "450px";
alertFram.style.height = "150px";
alertFram.style.background = "#ff0000";
alertFram.style.textAlign = "center";
alertFram.style.lineHeight = "150px";
alertFram.style.zIndex = "300";
strHtml = "
- \n";
strHtml += "
- \n"; strHtml += " \n"; strHtml += "
