php 中文网来的，见 https://www.php.cn/js-tutorial-397034.html
完整代码：
<!DOCTYPE html>
<html>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>js全屏和退出全屏代码</title>
<body>
<!-- requestFullScreen(document.documentElement): 整个网页进入全屏
requestFullScreen(document.getElementById("video-box")): 指定某块区域全屏
-->
<div id="abc">hello阿萨德</div>
<button onclick="requestFullScreen(document.documentElement)">全屏显示</button>
<button onclick="exitFull()">退出全屏</button>
</body>
<script type="text/javascript">
function requestFullScreen(element) {
// 判断各种浏览器，找到正确的方法
var requestMethod = element.requestFullScreen || //W3C
element.webkitRequestFullScreen || //Chrome等
element.mozRequestFullScreen || //FireFox
element.msRequestFullScreen; //IE11
if (requestMethod) {
requestMethod.call(element);
}
else if (typeof window.ActiveXObject !== "undefined") {//for Internet Explorer
var wscript = new ActiveXObject("WScript.Shell");
if (wscript !== null) {
wscript.SendKeys("{F11}");
}
}
}
function exitFull() {
// 判断各种浏览器，找到正确的方法
var exitMethod = document.exitFullscreen || //W3C
document.mozCancelFullScreen || //Chrome等
document.webkitExitFullscreen || //FireFox
document.webkitExitFullscreen; //IE11
if (exitMethod) {
exitMethod.call(document);
}
else if (typeof window.ActiveXObject !== "undefined") {//for Internet Explorer
var wscript = new ActiveXObject("WScript.Shell");
if (wscript !== null) {
wscript.SendKeys("{F11}");
}
}
}
</script>
</html>