> For the complete documentation index, see [llms.txt](https://anjia1.gitbook.io/web/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://anjia1.gitbook.io/web/browser/code/visibility.md).

# 页面是否激活

```js
// 字段名，有浏览器兼容性问题（这里先忽略）
if (typeof document.hidden !== "undefined") {
    hidden = "hidden"
    visibilityChange = "visibilitychange"
    state = "visibilityState"
}

// 关键代码
document.addEventListener('visibilitychange', function() {
    // 'hidden', 'visible'
    $vm.tab_visibility = document['visibilityState']
    if($vm.tab_visibility == 'visible'){
        EventBus.$emit('pg_visible')
        socketIO.revisible()
    }else{
        socketIO.rehide()
    }
}, false)

window.addEventListener('online',  () => {
    EventBus.$emit('pg_visible')
})
```