Navigator.onLine

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Returns the online status of the browser. The property returns a boolean value, with true meaning online and false meaning offline. The property sends updates whenever the browser's ability to connect to the network changes. The update occurs when the user follows links or when a script requests a remote page. For example, the property should return false when users click links soon after they lose internet connection.

Browsers implement this property differently.

In Chrome and Safari, if the browser is not able to connect to a local area network (LAN) or a router, it is offline; all other conditions return true . So while you can assume that the browser is offline when it returns a false value, you cannot assume that a true value necessarily means that the browser can access the internet. You could be getting false positives, such as in cases where the computer is running a virtualization software that has virtual ethernet adapters that are always "connected." Therefore, if you really want to determine the online status of the browser, you should develop additional means for checking. To learn more, see the HTML5 Rocks article, Working Off the Grid .

In Firefox and Internet Explorer, switching the browser to offline mode sends a false value. Until Firefox 41, all other conditions return a true value; testing actual behavior on Nightly 68 on Windows shows that it only looks for LAN connection like Chrome and Safari giving false positives.

You can see changes in the network state by listening for the events on window.ononline and window.onoffline .

句法

online = window.navigator.onLine;

值

online is a boolean true or false .

范例

视图 a live example .

To check if you are online, query window.navigator.onLine , as in the following example:

if (navigator.onLine) {
  console.log('online');
} else {
  console.log('offline');
}

If the browser doesn't support navigator.onLine the above example will always come out as false / undefined .

To see changes in the network state, use addEventListener to listen for the events on window.online and window.offline , as in the following example:

window.addEventListener('offline', function(e) { console.log('offline'); });
window.addEventListener('online', function(e) { console.log('online'); });

规范

规范	状态	注释
HTML 实时标准 The definition of 'navigator.onLine' in that specification.	实时标准	初始定义

浏览器兼容性

The compatibility table on this page is generated from structured data. If you'd like to contribute to the data, please check out https://github.com/mdn/browser-compat-data and send us a pull request. 更新 GitHub 上的兼容性数据

	桌面						移动
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	Android webview	Chrome for Android	Firefox for Android	Opera for Android	Safari on iOS	Samsung Internet
`onLine`	Chrome 1 1 Earlier versions of Chrome incorrectly return true when a tab is first opened, but it starts reporting the correct connectivity status after the first network event. Windows: 11, Mac: 14, Chrome OS: 13, Linux: Always returns `true` . For history, see crbug.com/7469 .	Edge 12	Firefox 3.5 3.5 Since Firefox 4 the browser returns `true` when 'Work Offline' mode is disabled and `false` when it is enabled, regardless of actual connectivity. Since Firefox 41, on OS X and Windows, the returned values follow the actual network connectivity, unless 'Work offline' mode is selected (where it will always return `false` ).	IE 8 8 in Internet Explorer 8 'online' and 'offline' events are raised on the `document.body` ; under IE 9 they are raised on both `document.body` and `window` .	Opera 3 3 From Opera 11.1 until Opera 12.1, the browser returns `true` when 'Work Offline' mode is disabled and `false` when it is enabled, regardless of actual connectivity.	Safari 5	WebView Android 1 1 Faulty in a WebView component, see Issue bug 16760 .	Chrome Android 18	Firefox Android 4	Opera Android 10.1 10.1 From Opera 11.1 until Opera 12.1, the browser returns `true` when 'Work Offline' mode is disabled and `false` when it is enabled, regardless of actual connectivity.	Safari iOS 4.2	Samsung Internet Android 1.0

图例

完整支持

注意事项

见 Online/Offline Events‎ for a more detailed description of this property as well as new offline-related features introduced in Firefox 3.

另请参阅

元数据

最后修改： Dec 5, 2019

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句法

值

范例

规范

浏览器兼容性

图例

注意事项

另请参阅

相关话题