IE方法：
document.frames['myFrame'].document.getElementById('test').value;
火狐方法：
document.getElementById('myFrame').contentWindow.document.getElementById('test').value;
IE、火狐方法：
function getValue(){
var tmp = '';
if(document.frames){
tmp += 'ie哥说：';
tmp += document.frames['myFrame'].document.getElementById('test').value;
}else{
tmp = document.getElementById('myFrame').contentWindow.document.getElementById('test').value;
}
alert(tmp);
}
示例代码：
a.html页面中的代码
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>
javascript 获取iframe里页面中元素的值 测试
</title>
</head>
<body>
<iframe id="myFrame" src='b.html' style="width:300px;height: 50px;"></iframe>
<input type="button" id="btn" onclick="getValue()" value="test" >
<script type="text/javascript">
function getValue(){
var tmp = '';
if(document.frames){
tmp += 'ie哥说：';
tmp += document.frames['myFrame'].document.getElementById('test').value;
}else{
tmp = document.getElementById('myFrame').contentWindow.document.getElementById('test').value;
}
alert(tmp);
}
</script>
</body>
</html>
b.html页面中的代码
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>
我是 iframe内的页面
</title>
</head>
<body>
<input type='text' id="test" value='欢迎访问：justflyhigh.com'>
</body>
</html>