offline, cross-tab communication (javascript-only)

Question

Is it possible to find foreign instances of certain website? Ofc theese are independently opened tabs (not by window.open). I need to prevent user from opening 2 tabs, and send message to previously opened tab to inform that it's impossible to open 2 tabs. 2 Intependent tabs may break page offline storage and webSQL structure, so that I can't allow people to use 2 tabs. It's also semi-offline app so it needs to be client-side solution.

Answer 1

You can communicate across tabs using localStorage. Every time you write a value, a "storage" event is fired on the window object on every tab (except the current one).

http://diveintohtml5.info/storage.html

Scroll down to "Tracking changes in the html5 storage area"

The event will include event.key, event.newValue, event.oldValue.

This only works in modern browsers.

Answer 2

In 2021, you can use service worker:

https://github.com/gyteng/service-worker-event

notice: service worker only works in https protocol

Answer 3

localStorage can be used to track windows. You should take into account a situation when window crashes - it will leave the garbage in localStorage. Accessing a common resource from several windows simultaneously may be done by mutex based on localStorage.

I've recently published the interwindow communication library (all features are described in readme). It provides thread-safe data sharing, cross-window locks and event broadcasting. It also solves some IE issues.

Answer 4

Broadcast Channel is design for this https://developer.mozilla.org/en-US/docs/Web/API/Broadcast_Channel_API

but the native api only support modern browsers. there is a npm package support all old browsers as well https://www.npmjs.com/package/broadcast-channel

Answer 5

You don't have control over that. The user can do basically whatever he/she wants on the computer.