Access to iframe subpages and parent page elements in html and access to js Variables

1. Access the parent page element parent.doc ument on the Child page. getElementById ('id') and document-related methods can be used in this way. 2. Access the child page element document on the parent page. getElementById ('iframeid '). contentDocument. getElementsByTagName ('table'); after contentDocument, you can use document-related methods. 3. Access the js variable on the parent page on the Child page. (Note: The js variable on the parent page must be a global variable) subpage var variable = parent. variableParent (variableParent is the variable defined on the parent page) 4. Access the js variable on the parent page. The current solution is to set global variables on the parent page, after modifying the child page, assign the variables on the Child page to the parent page.