<!-- 父窗口：http://www.domain.com/a.html -->

<iframe id="iframe" src="http://child.domain.com/b.html"></iframe>

<script> 

document.domain = 'domain.com';      

var user = 'admin';

</script>

<!-- 子窗口：http://child.domain.com/b.html -->

<script>  

document.domain = 'domain.com';      // 获取父窗口中变量  

alert('get js data from parent ---> '+ window.parent.user);

</script>