is-online

is-online

Check if the internet connection is up

Works in Node.js, CLI 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(callback)

callback(error, online)

Required
Type: function

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

Browser API

isOnline(callback)

callback(online)

Required
Type: function

CLI

$ npm install --global is-online

$ is-online --help

  Example
    $ is-online
    ✔︎ Online

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

License

MIT © Sindre Sorhus