html iframe 函数调用知识点

<div class="map_div">
        <iframe id='23d_page' marginwidth=0 marginheight=0 width="100%" height="100%" src="../indexCT.html"
            frameborder="no" class="3d_ct"></iframe>
        <!--<iframe id='25d_page' src="http://60.28.130.70:1008/ctpt/dgjl/mapcode/map.html" frameborder="0" width="100%"-->
            <!--height="100%" style="display: none" class="25d_ct"></iframe>-->
        <iframe id='25d_page' src="http://60.28.130.70:1008/ct25d/map.html" frameborder="0" width="100%"
        height="100%" style="display: none" class="25d_ct"></iframe>
        <div class="3d_img" style="position:absolute;z-index: 99;left: 1%;bottom: 2%;height: 9%;width: 6%;">
            <a href="#" class="open3d">
                <img src="./img/3d.png" alt="" style="width:100%;height: 100%;">
            </a>
        </div>
        <div class="25d_img" style="position:absolute;z-index: 99;left: 8%;bottom: 2%;height: 9%;width: 6%;">
            <a href="#" class="open25d">
                <img src="./img/25d.png" alt="" style="width: 100%;height: 100%;">
            </a>
        </div>
        <div class="2d_img" style="position:absolute;z-index: 99;left: 15%;bottom: 2%;height: 9%;width: 6%;">
            <a href="#" class="open2d">
                <img src="./img/电子地图.png" alt="" style="width:100%;height: 100%;">
            </a>
        </div>
    </div>
</div>

在当前网页，如果想调用iframe网页内的函数该怎么做呢？
通过document.getElementById('23d_page').contentWindow.functionName()来实现。