简单些，直接上代码了
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<meta http-equiv="X-UA-Compatible" content="ie=edge">
<title>Document</title>
</head>
<body>
//准备一个按钮
<button onclick="handleFullScreen()">全屏</button>
</body>
<script>
//定义一个变量进行判断，默认false 非全屏状态
let exitFullscreen = false
// 全屏事件
function handleFullScreen(){
let element = document.documentElement;
if (this.fullscreen) {
if (document.exitFullscreen) {
document.exitFullscreen();
} else if (document.webkitCancelFullScreen) {
document.webkitCancelFullScreen();
} else if (document.mozCancelFullScreen) {
document.mozCancelFullScreen();
} else if (document.msExitFullscreen) {
document.msExitFullscreen();
}
} else {
if (element.requestFullscreen) {
element.requestFullscreen();
} else if (element.webkitRequestFullScreen) {
element.webkitRequestFullScreen();
} else if (element.mozRequestFullScreen) {
element.mozRequestFullScreen();
} else if (element.msRequestFullscreen) {
// IE11
element.msRequestFullscreen();
}
}
}
</script>
</html>