function jianjie()
{
var ms=document.getElementsByTagName('span');
var obtn=document.getElementsByTagName('input');
var i=0;
for (var i = 0; i < obtn.length; i++)
{
obtn[i].index = i;
obtn[i].onclick= function ()
{
ms[this.index].style.display = 'block';
}
obtn[i].onmouseout=function ()
{
setTimeout(obtn[this.index].onmouseout=function () //这句按道理应该是setTimeout(function ()，但是写成这样就不能运行了。
{
ms[this.index].style.display = 'none';
},3000);
}
}
}
//主要目的是第三个input控制第三个SPAN的延迟隐藏与显示。
按照你的思路写了个完整的，应该是这样，几个改动地方有注释：
<!DOCTYPE HTML>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>无标题文档</title>
</head>
<body>
<div style="width:100px;height:100px;">
<span>234234</span>
</div>
<input type="button">
<script>
function jianjie() {
var ms = document.getElementsByTagName('span');
var obtn = document.getElementsByTagName('input');
var i = 0;
var timer
for (var i = 0; i < obtn.length; i++) {
obtn[i].index = i;
obtn[i].onclick = function () {
clearTimeout(timer); //保证点击时不会隐藏
ms[this.index].style.display = 'block';
}
obtn[i].onmouseout = function () {
clearTimeout(timer); //每次移出时确保只执行一个定时器
var a = this.index
//将this.index用a变量来保存，因为this.index只有在事件触发时才会有值，如果设置了settimeout就是undefined，因此用变量将它保存起来
timer = setTimeout(function () {
ms[a].style.display = 'none';
}, 3000);
}
}
}
jianjie()
</script>
</body>
</html><!DOCTYPE HTML>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>无标题文档</title>
</head>
<body>
<div style="width:100px;height:100px;">
<span>234234</span>
</div>
<input type="button">
<div style="width:100px;height:100px;">
<span>234234</span>
</div>
<input type="button">
<div style="width:100px;height:100px;">
<span>234234</span>
</div>
<input type="button">
<script>
function jianjie() {
var ms = document.getElementsByTagName('span');
var obtn = document.getElementsByTagName('input');
var i = 0;
var timer
for (var i = 0; i < obtn.length; i++) {
obtn[i].index = i;
obtn[i].onclick = function () {
clearTimeout(obtn[this.index].timer); //保证点击时不会隐藏
ms[this.index].style.display = 'block';
}
obtn[i].onmouseout = function () {
clearTimeout(obtn[this.index].timer); //每次移出时确保只执行一个定时器
var a = this.index
//将this.index用a变量来保存，因为this.index只有在事件触发时才会有值，如果设置了settimeout就是undefined，因此用变量将它保存起来
obtn[this.index].timer = setTimeout(function () {
ms[a].style.display = 'none';
}, 3000);
}
}
}
jianjie()
</script>
</body>
</html>