The difference between window.parent and Window.opener

Window.parent can get a frame's parent window or parent frame. The parent of the top-level window refers to itself.

You can use this feature to determine whether the window is a top-level window. Such as:

Code
function Istopwindow (Win)
{
if (win.parent = win) return true;
else return false;
}
Window.opener refers to the parent page of the window.open open page.

Opener that who opened my, such as a page using window.open pop-up b page window, then a page is the window is the B page opener, the B page through the opener object can access a page.
Parent represents the parents window, such as a page with an IFRAME or frame to invoke B page, then page A is the parent of page B.
In JS, Window.opener is just a reference to the pop-up window's parent window. Like what:

In A.html, window.open a new window b.html by clicking on a button. Then in b.html, we can use Window.opener (omit write as opener) to reference a.html, including a.html document and other objects, manipulate a.html content. If this reference fails, then NULL is returned. Therefore, before calling the opener object, you must first determine whether the object is null, otherwise the "object is empty or does not exist" JS error.

Window.opener returns a reference to the window that created the current window, such as clicking a link on the a.htm and opening the b.htm, and then we're going to enter a value on the b.htm and give it a TextBox with ID "name" on the a.htm. It can be written as:
Window.opener.document.getElementById ("name"). Value = "entered data";