Returns the number of frames (either <frame> or <iframe> elements) in the window. 
A number.
js
if (window.length) { // this is a document with subframes }
| Specification | 
|---|
| HTML Standard  # dom-length-dev  | 
| Desktop | Mobile | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Chrome | Edge | Firefox | Internet Explorer | Opera | Safari | WebView Android | Chrome Android | Firefox for Android | Opera Android | Safari on IOS | Samsung Internet | |
length | 
1 | 12 | 1 | 4 | ≤12.1 | 1 | 4.4 | 18 | 4 | ≤12.1 | 1 | 1.0 | 
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    https://developer.mozilla.org/en-US/docs/Web/API/Window/length