Popups and Window Methods

Popups are separate browser windows opened via JavaScript. While often abused for ads, they’re legitimate for OAuth logins, file pickers, and multi-window apps.

Opening a Popup

const popup = window.open(url, name, params);

// Open a small popup
const win = window.open(
  'https://example.com',
  'myPopup',
  'width=400,height=300,left=100,top=100'
);

Window Features

Controlling the Popup

Once you have a reference to the popup window:

// Move/resize
win.moveTo(100, 100);
win.moveBy(50, 50);
win.resizeTo(500, 400);
win.resizeBy(50, 50);

// Scroll
win.scrollTo(0, 200);

// Focus/blur
win.focus();
win.blur();

// Close
win.close();

<div id='popup-demo' style='padding:16px;background:#f1f5f9;border-radius:8px;'>
<p style='margin-bottom:8px;'>Popup will open in a new window.</p>
<div style='display:flex;gap:8px;flex-wrap:wrap;'>
<button id='open-popup'>Open Popup</button>
<button id='resize-popup'>Resize (400x300)</button>
<button id='move-popup'>Move (200, 200)</button>
<button id='close-popup'>Close Popup</button>
</div>
<pre id='popup-log' style='background:white;padding:8px;border-radius:4px;margin-top:8px;'></pre>
</div>

const log = document.getElementById('popup-log');
let popup = null;

document.getElementById('open-popup').onclick = function() {
if (popup && !popup.closed) {
log.textContent = 'Popup already open';
return;
}
popup = window.open('', 'demoPopup', 'width=300,height=200,left=300,top=200');
popup.document.write('<h2>Hello from popup!</h2><p>This window is controlled by the parent.</p><button onclick='window.close()'>Close Me</button>');
popup.document.title = 'Demo Popup';
log.textContent = 'Popup opened at ' + new Date().toLocaleTimeString();
};

document.getElementById('resize-popup').onclick = function() {
if (popup && !popup.closed) {
popup.resizeTo(400, 300);
popup.focus();
log.textContent = 'Resized popup to 400x300';
} else {
log.textContent = 'No popup open';
}
};

document.getElementById('move-popup').onclick = function() {
if (popup && !popup.closed) {
popup.moveTo(200, 200);
popup.focus();
log.textContent = 'Moved popup to (200, 200)';
} else {
log.textContent = 'No popup open';
}
};

document.getElementById('close-popup').onclick = function() {
if (popup && !popup.closed) {
popup.close();
popup = null;
log.textContent = 'Popup closed';
} else {
log.textContent = 'No popup to close';
}
};

Popup Blocker

Browsers block popups that aren’t triggered by user action. Popups opened on page load are blocked. Only open popups in direct response to a user click:

// OK - user gesture
button.addEventListener('click', () => window.open(url));

// Blocked - no user gesture
window.open(url); // blocked by most browsers

Checking if a Popup Was Blocked

const win = window.open(url);
if (!win || win.closed) {
  alert('Popup was blocked! Please allow popups for this site.');
}

The window.opener Property

A popup can access its parent via window.opener:

// In the popup:
window.opener.document.body.style.background = 'yellow';

Modern browsers restrict cross-origin opener access. Use noopener for security:

<a href="page.html" target="_blank" rel="noopener">Safe link</a>

Window Methods Overview

Key Takeaways

• Open popups only in direct response to user clicks (bypass blocker)
• Use window.open() with feature params for size and position
• The popup window is a Window object - you can control and inspect it
• Popups can access the opener via window.opener (same-origin only)
• Always handle the popup blocked case gracefully
• For modern apps, prefer modals or <dialog> over popups for better UX