What is the global length variable (window.length)?

Question

I have just observed that every page has length global variable.

What does this variable represent? Is it somehow related to how many iframes/frames are loaded on page?

It'd be happy if a doc reference is provided.

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For example, on Chrome new tab page its value is 17 and here, on StackOverflow it is 0.

Answer 1

Yes, it's how many frames (including iframes) are in the current window:

https://developer.mozilla.org/en-US/docs/Web/API/Window.length

W3 specification:

http://www.w3.org/html/wg/drafts/html/master/browsers.html#accessing-other-browsing-contexts

Answer 2

window.length

Returns the number of frames (either frame or iframe elements) in the window.

Example

if (window.length) {
  // this is a document with subframes
}

MDN Reference

Note: No part of this answer comes from me. It all comes from the referred source.