is-online

is-online

Check if the internet connection is up

Works in Node.js and the browser (with browserify).

In the browser you have navigator.onLine, but it's useless as it only tells you if there's a local connection, and not whether the internet is accessible.

Install

$ npm install --save is-online

Usage

var isOnline = require('is-online');

isOnline(function(err, online) {
	console.log(online);
	//=> true
});

Node API

isOnline([options], callback)

options

Optional
Type: object

timeout

Type: number

Default: 2000

Milliseconds to wait for a server to send response.

hostnames

Type: string, array

Default: ['www.google.com', 'www.cloudflare.com', 'www.baidu.com', 'www.yandex.ru']

One or more hosts to check.

callback(error, online)

Required
Type: function

error is there only by Node.js convention and is always null.

Browser API

Same as above except the callback doesn't have an error parameter.

How it works

In node, we first contact one of the thirteen root servers and ask them to direct us to the servers which host the <root> zone (Which they are themselves). If the server answers, we return an online status.

If no satisfying answer is given within one second, we return an offline status. In the rare case where an firewall intercepts the packet and answers it on its behalf, a second check is run which tries to connect to a series of popular web sites on port 80. If one of these connects, we return online, otherwise offline status.

In the browser, a sophisticated check like in node is not possible because DNS and sockets are abstracted away. We use a check which requests an uncached favicon.ico on a series of popular websites. If one of this checks succeeds, we return online status. If all the requests fail, we return offline status.

Contributors

• silverwind

Related

• is-online-cli - CLI for this module
• is-reachable - Check if servers are reachable

License

MIT © Sindre Sorhus