1. Get the elements of the parent page in the iframe sub-page:
a>window.parent.document is to get the object in the parent page document;
b> If you want to get the method in the parent page js: window.parent.xxxx(); xxxx() is a method;
2. Get the elements in the iframe subpage in the parent page:
a>
var child = document.getElementByIdx_x("mainFrame").contentWindow;//mainFrame id is the id of the parent page iframe
child.document;//Get the document object in the child page;