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How do I invoke an event on a Parent window from a Child window

I have a Parent window that displays information, including a link to open a Child window to edit the same information. I want to be able to either refresh the Parent window or activate a button on the Parent to re-select the data, when the Child window is being closed. Both programs are written in PHP.
The Parent program opens the Child window using the following JavaScript function:
function windowOpen(loadURL) {
// In order to allow JavaScript to Close the Window, the Windows needs to be
// opened with JavaScript. The URL to be loaded into the new Window is passed
// as a parameter.
window.open(loadURL, "_blank");
}
The Child program currently uses this JavaScript function to close itself:
function windowClose() {
window.open('','_parent','');
window.close();
}
How do I change the windowClose() function to either: i) Refresh the Parent window; or ii) click a button on the Parent page that will re-select and re-display the page.
Thank you in advance.

It's not clear what you are trying to achieve but try
cross window communication

Why does my popup window lose its event beforeunload after a reload?

I have a small application that opens a new popup. I store the window in a variable:
popup = window.open("sites/display.html", "_blank");
After that I add a beforeunload Eventlistener:
$(popup).on('beforeunload', function(){
// Do something
});
I then later reload the window with a button:
popup.location = popup.location;
After that if I close the window the Event beforeunload isn't fired anymore. I think it has something to do with the reload because if I dont reload the page everything works fine.
How can I fix this so the event is fired everytime the window closes?
Exact code I use:
function startClock(allowRestart) {
saveSettings(allowRestart);
if ($("#separated-display").is(":checked")) {
// Separated mode activated
if (popup == undefined) {
openPopup();
} else {
if (popup.closed) {
openPopup();
}else{
popup.location.reload();
}
}
} else {
// Separated mode deactivated
if (popup != null && popup.closed == false) {
$(popup).unbind();
popup.close();
}
window.location = "sites/display.html"; // Open the clock in same window
}
}
function openPopup(){
// Open new popup window
popup = window.open("sites/display.html", "_blank");
// TO-DO: Fix event not fired after 1. window reload 2. window close
popup.addEventListener('beforeunload', function(){
console.log("unload");
});
}

As you're trying to access the same origin (with the relative path) window using window.open(), Access error shouldn't be displayed.
popup = window.open("/sites/display.html", "_blank")
popup variable would refer to the newly created window which is a thin wrapper representing a WindowProxy object, which indeed has all features of window available.
When the page reloads everything is set to default, and the window loses its properties set before. Therefore, the unload event attached earlier is not anymore attached. This would happen for other events as well.
Hence the problem here that the event is being attached to the popup window just once on opening the popup, which is reset on page reload. The best way to go forward would be to add the unload event in the js file which loads specifically on sites/display.html page. There, every time when sites/display.html page loads you could access the new window object and attach events in window.load / document.ready (according to your use case).
You won't able to attach the event to pop up before or after invoking page reload as you're doing it currently as, the property would be reset if you try setting it before/after page reload as it might be executed asynchronously.
NOTE:
You should rather use the reload() function exposed by window.location instead of updating the location property. As updating the property doesn't skip browser cache.
popup.location.reload()
The support for window.open is unknown for most browsers, though I was able to use it on Chrome 84.

How do I close the current browser tab on ReactJS?

Basically, I want the current browser tab to be closed on a click of a button. How do I implement this in ReactJS? Tried window.close() but did not work.

For security purposes, JavaScript can't close a window that it didn't directly open.
https://developer.mozilla.org/en-US/docs/Web/API/Window/close
As you can see from the example, the originating script (which opened the window) must also be the script that closes the window. A new window isn't capable of closing itself via JavaScript.
//Global var to store a reference to the opened window
var openedWindow;
function openWindow() {
openedWindow = window.open('moreinfo.htm');
}
function closeOpenedWindow() {
openedWindow.close();
}

On your click event handler, try this :
window.open("", "_self");
window.close();

Refresh parent window when the pop-up window is closed

Is there any way I can refresh the parent window when a popup window is closed without adding any javascript code to the popup window?
I have a page parent.php on which users can click "open popup" to open a popup window. This popup window shows some flash content and its not possible for me to add something like
window.onunload = function(){
window.opener.location.reload();
};
to the popup window page markup.
Is there any other method to achieve this?
Thanks

To make this work in all major browsers, you need to handle the unload event handler in the pop-up and do the reloading in the main window. In the main window, add
function popUpClosed() {
window.location.reload();
}
In the pop-up:
window.onunload = function() {
if (window.opener && !window.opener.closed) {
window.opener.popUpClosed();
}
};
So the answer to your question is generally no, if you need your code to work in all browsers, in particular IE.

I'm sure you can just add this to parent.php:
var myPop = "pop up window selector"
myPop.onunload = function(){
location.reload();
};

The problem with Tim Down's method is that it doesn't answer the original question. The requirement is that you cannot add any code to the pop-up window.
One solution that I've found, while not particularly elegant, is effective across all browsers I've tested on.
You will be simply polling the newly created window object continuously, checking if it's still open.
On parent window:
var register;
var poll;
function isOpen(){
if(register.closed){alert("Closed!"); clearInterval(poll);}
}
function create(){
register = window.open("http://www.google.com","register","width=425,height=550");
poll=setInterval("isOpen()",100); //Poll every 100 ms.
}

had similar problem to detect the closing popup in the parent window. I think the reason was
in not setting the document.domain property.
any way add to Tim Down answer the document.domain property for both window and popup like this:
<script type="text/javascript">
document.domain='<?=$_SERVER['SERVER_NAME']?>';
</script>
and instead of
window.onunload = function() {
if (window.opener && !window.opener.closed) {
window.opener.popUpClosed();
}
};
I used in the popup :
<body onunload="window.opener.popUpClosed();">

Find window previously opened by window.open

We've got the following situation, running from a single domain:
Page A uses window.open() to open a named window (a popup player). window.open() gives page A a reference to the window.
User now reloads page A. The reference to the named window is lost. Using window.open() to "find" the window has the unfortunate side effect of reloading it (undesirable). Is there any other way to get a reference to this window?

Try this:
var playerUrl = 'http://my.player...';
var popupPlayer= window.open('', 'popupPlayer', 'width=150,height=100') ;
if(popupPlayer.location.href == 'about:blank' ){
popupPlayer.location = playerUrl ;
}
popupPlayer.focus();
It will open a blank window with a unique name. Since the url is blank, the content of the window will not be reloaded.

AFAIK, no there isn't..
A kind-of-dirty-but-i-guess-it-will-work hack would be to periodically reset the reference on the parent window from within the popup using window.opener, with something like this code:
setInterval(function() {
if(window.opener) {
window.opener.document.myPopupWindow = window
}
}, 100)
In the parent window, you'll be able to access document.myPopupWindow, even after a reload (well, 100ms after the reload). This should work cross browser.

Actually what you did is destroy the parent (page A) of the created window (Popup), so it has no more reference to the original parent therefore you can't get a direct reference.
The only solution I can think of is using a browser that offers you added javascript capability to cycle through active windows (tabs) and find one that has a special property (ie: your reloaded page A) that gets recognized by the popup.
Unfortunately I guess only firefox has some added capability or extension that gives you this flexibility. (it is also a security risk though)

This should work. Add this code in the popup:
function updateOpener() {
if (window.opener)
window.opener.document.myPopupWindow = window;
else
setTimeout(updateOpener, 100);
}
updateOpener();
And this in onload of the parent window. To make sure myPopupWindow have been set wait 100 ms before accessing it.
setTimeout(function() {
if (document.myPopupWindow)
document.myPopupWindow.focus();
}, 100);

If all the windows share a common Url origin you can register a ServiceWorker and then access all windows from the ServiceWorker: https://developer.mozilla.org/en-US/docs/Web/API/Clients
AFAIK You won't be able to pass a reference to other windows from WorkerService to your window but you can establish communications with the ServiceWorker via
https://developer.mozilla.org/en-US/docs/Web/API/Worker/postMessage
https://developer.mozilla.org/en-US/docs/Web/API/Client/postMessage

It Might help someone, If you opened an child tab and after refreshing the parent tab, you still want to focus on that child tab instead of opening new child tab: -
const chatPopup = window.open('', 'chatPopup');
if (chatPopup.location.href === 'about:blank' || !chatPopup.location.href.includes('/chat')) {
this.openNewWindow = window.open('/chat', 'chatPopup');}