JavaScript shows Div across frames

The project encountered the need to cross-frame display div problem, Baidu a bit, collected a bit of wisdom of the masses, special sorting out the following example, first look at:

In this case there are 4 pages:

Index.html

Frame.html
<frameset rows= "74,*" cols= "*" style= "z-index:1" >        <frame src= "frame-top.html" style= "Z-index:1" >        <frame src= "frame-main.html" style= "z-index:1" > </frameset><noframes></noframes>
Frame-top.html
<a href= "#" onclick= "Top.document.getElementById (' Popid '). style.display= ' Block ' >show div</a>

Frame-main.html
I ' m main frame

The page is set up, directly open index.html can see the effect. The specific principle is to display the div of the parent page from inside the frame by setting the div on the parent page.
JavaScript shows Div across frames