捕获按钮单击Iframe内部的事件 - 角度

Question

<button class="btn btn-default" ng-click="openModal()">Open Iframe</button>

<div id="omniScriptModal" class="modal">
    <div class="iframe-close" ng-click="closeModal()">Close</div>
    <iframe id="omniScriptIFrameModal" frameborder="0" allowfullscreen 
            src="ExternalLink"></iframe>
</div>

Iframe有标签，点击标签内的某个按钮，我需要模型 omniScriptModal 才能关闭。

$scope.openModal = function(){
    document.getElementById('omniScriptModal').style.zIndex = 1040;

    var buttonComponent = document.getElementById('omniScriptIFrameModal').contentWindow.document.getElementById('IdentifyCaller_nextBtn');

    buttonComponent.onclick = function ($scope) {
            document.getElementById('omniScriptModal').style.zIndex = -1;
        }
    }

上面代码中的问题是，如果按钮加载很晚则不起作用或如果iframe中的按钮位于其他内容中标签