jQuery isWindow() Method

What Is isWindow()?

jQuery.isWindow(obj) (alias $.isWindow) returns true when obj is a browser window — the current page window or an iframe’s contentWindow (added in jQuery 1.4.3).

$.isWindow(obj)  → true | false

$.isWindow(window)  // true
$.isWindow({})      // false
$.isWindow(document.body)  // false

// Official replacement (jQuery 3.3+):
function isWindow(obj) {
  return obj != null && obj === obj.window;
}

How to Use isWindow()

Pass a candidate object; branch when it is a browsing context window.

1. Start with a value that might be a window (context arg, iframe handle, etc.).
2. Call $.isWindow(obj) — or the official one-liner replacement.
3. If true, treat it as a window (read document, size, location, …).
4. If false, handle as a normal object or DOM node instead.

Pseudocode

function isWindow(obj):
    // official jQuery recommendation
    return obj != null and obj === obj.window

// Typical use:
if isWindow(context):
    doc = context.document
else:
    // treat as element / plain object / other

Cheat Sheet

Keep these facts handy while detecting window objects with jQuery.

Live Preview

Pick a sample value and see what $.isWindow() returns.

$.isWindow(window)
→ true

/* current browsing context */

jQuery Examples

Short, copy-ready snippets. Open DevTools Console, or use Try It Yourself for a live editor.

console.log($.isWindow(window));              // true
console.log(window === window.window);        // true
console.log($.isWindow(self));                // true (same window)

true
true
true

console.log($.isWindow({}));              // false
console.log($.isWindow(document));        // false
console.log($.isWindow(document.body));   // false
console.log($.isWindow(null));            // false

false
false
false
false

function isWindow(obj) {
  return obj != null && obj === obj.window;
}

console.log(isWindow(window));  // true
console.log(isWindow({}));      // false
console.log($.isWindow(window) === isWindow(window));  // true

true
false
true

// <iframe id="frame" src="about:blank"></iframe>
var frame = document.getElementById("frame");
var win = frame.contentWindow;

console.log($.isWindow(win));   // true
console.log($.isWindow(frame)); // false (element, not window)

true
false

Performance Notes

The check is a couple of property reads. Cost is never the issue — correctness (and same-origin iframe access) is.

Key Takeaways