EDIT

Parent window HTML

<script language="JavaScript" type="text/javascript">
function openPopUP() {
  window.open('mywindow.html','NewWin',
            'toolbar=no,status=no,width=350,height=135')
}
</script>

<body onLoad="openPopUP();">
or
<a href="javascript:openPopUP();">Click to open popup</a>

Child Window i.e PopUp Window File

The below script should be in the child window. The child window will open and will automatically be hidden after 1 second. The value 1000 specified in the setTimeout method is the duration in milliseconds for which the child window will be open. You can increase this timeout duration if you want the child window to be open longer.

<body onLoad="setTimeout('window.blur()', 1000);" 
          onFocus="setTimeout('window.blur()', 1000);">

This might work for you: Add this line of code in the onload event of your child window...

window.parent.opener.focus(); 
Answer from Pranay Rana on Stack Overflow
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Stack Overflow
stackoverflow.com › questions › 52840251 › javascripts-window-open-method-with-screen-size-mode-is-still-opening-browser
JavaScript's Window.Open() method with screen size mode is still opening browser window in minimized mode - Stack Overflow
Window.Open() method in the following file is still opening the browser window in minimized mode, you still have to click the maximize button on the top right corner of the newly opened window to maximize it.
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Wrox
p2p.wrox.com › javascript-how › 18925-popup-window-automatically-minimized-click.html
Popup window automatically minimized on click!
Hello, I have a popupwindow defined as followed: function popupPage(prgName) { windowprops = "height=300,width=450,location=no," + "scro
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MDN Web Docs
developer.mozilla.org › en-US › docs › Web › API › Window › open
Window: open() method - Web APIs | MDN
By default, window.open opens the page in a new tab. If popup is set to true, it requests that a minimal popup window be used. The UI features included in the popup window will be automatically decided by the browser, generally including an address bar only.
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Experts Exchange
experts-exchange.com › questions › 11565678 › open-minimized-window-with-javascript.html
Solved: open minimized window with javascript | Experts Exchange
August 14, 1999 - If I havn't misunderstood you, this is the code you wanted (no change to the function): <a href="javascript:;" onClick="if (newWin) { newWin.focus(); } else { launch('mytitle',100,100,' http://www.firstsite.com');}">open the window</a>(then minimize it)<br> <a href="javascript:;" onClick="if (newWin) {newWin.location='http://www.secondsite.com';newWin.focus(); }">bring it to front</a> Regards, Mårten
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Plus2Net
plus2net.com › javascript_tutorial › blur.php
window.blur to lose focus and to minimize window
<html> <head> <meta http-equiv="Content-Type" content="text/html; charset=windows-1252"> <title>Demo of blur and focus of a window</title> <script language=javascript> function to_close(){ tm.close(); } function to_open(){ tm=window.open("moveby-child.htm","Ratting","width=250,height=150,left=150,0,top=200,status=0,"); } function to_focus(){ tm.focus(); // Keeping the focus on small window } function to_blur(){ tm.blur(); // Keeping the focus out on small window } ////////////////// function display_c(){ var refresh=1000; // Refresh rate in milli seconds mytime=setTimeout('display_msg()',refre
Find elsewhere
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Stack Overflow
stackoverflow.com › questions › 46617619 › javascript-open-new-popup-window-but-in-minimized-mode
jquery - javascript open new popup window but in minimized mode - Stack Overflow
let popup = window.open('', "s", "width=720;height=300;left=300;top=300;resizable=yes;toolbar=no;location=no;directories=no;status=no;menubar=no;scrollbars=yes;resizable=no;copyhistory=no").blur(); window.focus();
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JavaScript.info
javascript.info › tutorial › frames and windows
Popups and window methods
They only work reliably on popups that we opened, that have no additional tabs. ... JavaScript has no way to minify or maximize a window. These OS-level functions are hidden from Frontend-developers.
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MDN Web Docs
developer.mozilla.org › en-US › docs › Mozilla › Add-ons › WebExtensions › API › windows › WindowState
windows.WindowState - Mozilla | MDN
JavaScript APIs · windows · windows.WindowState · Theme · OS default · Light · Dark · English (US) Remember language · Learn more · Deutsch · English (US) Français · 日本語 · 中文 (简体) The state of this browser window. Values of this type are strings. Possible values are: "normal" The window is at the default size or user-selected size. "minimized" The window is only visible as an icon in the taskbar.
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Coderanch
coderanch.com › t › 632118 › languages › minimize-browser-window-minimize-button
how to minimize browser window on minimize button click (HTML Pages with CSS and JavaScript forum at Coderanch)
There isn't a method to minimize the window in the way you want. You can make it very small. You can stop it from being in full screen mode. You can do what you are already doing.
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Experts Exchange
experts-exchange.com › questions › 20974858 › window-open-remove-minimize-and-maximize-buttons-from-popup.html
Solved: window.open remove minimize and maximize buttons from popup | Experts Exchange
March 26, 2004 - I don't want the user to minimize, maximize (or resize) the window ... and they can't as it stands now, but I'd prefer if the minimize button was also disabled. Is there anyway to accomplish this? I've searched high and low for this so I really appreciate the help. Thanks. window.open("foo.htm", "", "modal=1, height=200, width=200"); FYI - I removed all the of the other attributes that were mentioned in the original question as they seemed to have no effect.
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Tek-Tips
tek-tips.com › home › forums › software › programmers › web development › javascript
HOW TO MINIMIZE A POP UP WINDOW? | Tek-Tips
November 15, 2001 - found it, but it doesnt work properly in netscapes.. so, i lied here: function op(){ win1=window.open(&quot;somedoc.html&quot;,&quot;hidden&quot;,&quot;left=2000,top=2000,width=10,height=10&quot; } Victor ... I seem to recall that the minimum size is something like 100x100 pixels.
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HTML Goodies
htmlgoodies.com › home › javascript
Minimize/Maximize a Browser Window | HTML Goodies
January 4, 2005 - Please understand you must be running Netscape Navigator 4 or better to see it. Once you click “minimize”, wait one moment. Not only will the screen get smaller, it’ll jump to the bottom right portion of the screen. It’s really a neat effect. Click me · <SCRIPT LANGUAGE=”JavaScript”> ...
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Coderanch
coderanch.com › t › 116202 › languages › restore-minimized-window
restore minimized window (HTML Pages with CSS and JavaScript forum at Coderanch)
thanks for your immediate reply, but i have called popup window using window.open(url,...) it is working fine. my thing is that, suppose we have not closed the popup window we just minimized the popup window.(it is opend) now again i call the popup window on mainwindow.
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Openfin
cdn.openfin.co › docs › javascript › 30.110.74.13 › tutorial-Window.minimize.html
OpenFin JavaScript API - Tutorial: Window.minimize
async function minWindow() { const win = await fin.Window.getCurrent(); return await win.minimize(); } minWindow().then(() => console.log('Minimized window')).catch(err => console.log(err));