下面代码为什么“一级栏目”要点击两次才出来二级栏目,谢谢!
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=gb2312" />
<title>无标题文档</title>
</head><body>
<div><a href="javascript: change(1)"> 一级栏目</a></div>
<ul id="1" style="display:none">
<li>二级栏目</li>
<li>二级栏目</li>
<li>二级栏目</li>
<li>二级栏目</li>
</ul>
<script language="javascript">
//栏目变换
function change(n)
{
if(document.getElementById(n).value=="0")
{
document.getElementById(n).style.display="";
document.getElementById(n).value="1";
}
else{
document.getElementById(n).style.display="none";
document.getElementById(n).value="0";
}
}
</script>
</body>
</html>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=gb2312" />
<title>无标题文档</title>
</head><body>
<div><a href="javascript: change(1)"> 一级栏目</a></div>
<ul id="1" style="display:none">
<li>二级栏目</li>
<li>二级栏目</li>
<li>二级栏目</li>
<li>二级栏目</li>
</ul>
<script language="javascript">
//栏目变换
function change(n)
{
if(document.getElementById(n).value=="0")
{
document.getElementById(n).style.display="";
document.getElementById(n).value="1";
}
else{
document.getElementById(n).style.display="none";
document.getElementById(n).value="0";
}
}
</script>
</body>
</html>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=gb2312" />
<title>无标题文档</title>
</head><body>
<div><a href="javascript: change(1)"> 一级栏目</a></div>
<ul id="1" style="display:none">
<li>二级栏目</li>
<li>二级栏目</li>
<li>二级栏目</li>
<li>二级栏目</li>
</ul>
<script language="javascript">
//栏目变换
function change(n)
{
if(!document.getElementById(n).value || document.getElementById(n).value=="0")
{
document.getElementById(n).style.display="";
document.getElementById(n).value="1";
}
else{
document.getElementById(n).style.display="none";
document.getElementById(n).value="0";
}
}
</script>
</body>
</html>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=gb2312" />
<title>无标题文档</title>
</head><body>
<div><a href="javascript: change(1)"> 一级栏目</a></div>
<ul id="1" style="display:none">
<li>二级栏目</li>
<li>二级栏目</li>
<li>二级栏目</li>
<li>二级栏目</li>
</ul>
<script language="javascript">
//栏目变换
function change(n)
{
if(document.getElementById(n).value==null||document.getElementById(n).value=="0")
{
document.getElementById(n).style.display="";
document.getElementById(n).value="1";
}
else{
document.getElementById(n).style.display="none";
document.getElementById(n).value="0";
}
}
</script></body>
</html>出现问题原因:
LZ的ul并没有定义value属性,所以第一次获取该组件的value值是null