Fullscreen requires user interaction to initiate. It's a security feature.
Imagine if some pop-up could force you into fullscreen mode, lock your mouse pointer, and start playing an advertisement without your permission.
Having a 'enable full screen' link or button who's visibility is toggled in the document 'fullscreenchange' event handler seems like a practical approach.
与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…