leader election plugin to choose master tab among all same cross origin tabs
Common case for leader election is long-polling apps. jleader lets you offload server and client by sending connections only from leader tab. Usage:
//Subscribe to leader updates. Callback will be fired when current tab changes it's state.
leader.subscribe(function(newValue) {
if (newValue) {
alert('This tab became master');
} else {
//Tab can lose it's master state if another tab use forces (explicitly calls electMe())
alert('This tab is not master anymore');
}
});
//Announce this tab as a peer. Check whether master is online. If not - elect this tab as master
leader.announce();
//current state is stored here
if (!leader.isMaster) {
//You can force this tab to become master
leader.electMe()
}Plugin is based on HTML5 localStorage fire state event. jStorage is used underneath. Shared Worker is the best approach but it's not yet implemented in major browsers. Code should work in all browsers that are supported by jStorage but not all of them were tested.
Tested browsers:
- Chrome (24+)
- Firefox (18+)
- Safari (6+)
- IE (9+)
Warning jleader is not thread safe as localStorage is not thread safe among different tabs. However everything works just fine. There is a mutex implementation and it will be added if someone encounters problems with thread safeness.