浏览器各事件
1、浏览器切换事件 visibilitychange
document.addEventListener('visibilitychange', () => {
if(document.visibilityState === "hidden") {
document.title = "喂，你人呢？"
}
if(document.visibilityState === "visible") {
document.title = "哎呀，你回来啦！"
}
})
2、浏览器关闭事件 beforeunload
window.addEventListener('beforeunload',()=>{
console.log('啊？你要走了啊！')
})
3、浏览器刷新事件 onload
window.addEventListener('onload',()=>{
console.log('刷一刷！浪一浪！')
})