The read-only fullscreenEnabled property on the Document interface indicates whether or not fullscreen mode is available.

fullscreen mode is available only for a page that has no windowed plug-ins in any of its documents, and if all <iframe> elements which contain the document have their allowfullscreen attribute set.

Although this property is read-only, it will not throw if it is modified (even in strict mode); the setter is a no-operation and it will be ignored.

A boolean value which is true if the document and the elements within can be placed into fullscreen mode by calling Element.requestFullscreen(). If fullscreen mode isn't available, this value is false.

In this example, before attempting to request fullscreen mode for a <video> element, the value of fullscreenEnabled is checked, in order to avoid making the attempt when not available.

function requestFullscreen() {
  if (document.fullscreenEnabled) {
    videoElement.requestFullscreen();
  } else {
    console.log("Your browser cannot use fullscreen right now");
  }
}

• Fullscreen API
• Guide to the Fullscreen API
• Element.requestFullscreen()
• Document.exitFullscreen()
• Document.fullscreenElement
• :fullscreen and ::backdrop
• The <iframe> allowfullscreen attribute