Cross-tab window communication

dispatcher.js

function Dispatcher(channel_name, broadcast_to_self) {
    this.channel_name = channel_name ? 'dispatcher:' + channel_name : 'dispatcher:default_channel';
    this.id = Math.random();
    this.isMaster = false;
    this.others = {};
    this.broadcast_to_self = broadcast_to_self === undefined ? true || !!broadcast_to_self;
    this.callbacks = {};

    window.addEventListener( 'storage', this, false );
    window.addEventListener( 'unload', this, false );

    this.broadcast( 'hello' );

    var that = this;
    var check = function check () {
        that.check();
        that._checkTimeout = setTimeout( check, 9000 );
    };
    var ping = function ping () {
        that.sendPing();
        that._pingTimeout = setTimeout( ping, 17000 );
    };
    this._checkTimeout = setTimeout( check, 500 );
    this._pingTimeout = setTimeout( ping, 17000 );
}

Dispatcher.prototype.destroy = function () {
    clearTimeout( this._pingTimeout );
    clearTimeout( this._checkTimeout );

    window.removeEventListener( 'storage', this, false );
    window.removeEventListener( 'unload', this, false );

    this.broadcast( 'bye' );
};

Dispatcher.prototype.handleEvent = function ( event ) {
    if ( event.type === 'unload' ) {
        this.destroy();
    } else if ( event.key === this.channel_name ) {
        var data = JSON.parse( event.newValue ), type = data.type;
        switch ( type ) {
            case 'ping':
            case 'hello':
            case 'bye':
                this[ type ]( data );
                break;
            default:
                try {
                   this.callbacks[ type ].call( this, data );
                }
                catch ( error ) {}
        }
    }
};

Dispatcher.prototype.sendPing = function () {
    this.broadcast( 'ping' );
};

Dispatcher.prototype.hello = function ( event ) {
    this.ping( event );
    if ( event.id < this.id ) {
        this.check();
    } else {
        this.sendPing();
    }
};

Dispatcher.prototype.ping = function ( event ) {
    this.others[ event.id ] = +new Date();
};

Dispatcher.prototype.bye = function ( event ) {
    delete this.others[ event.id ];
    this.check();
};

Dispatcher.prototype.check = function ( event ) {
    var now = +new Date(),
        takeMaster = true,
        id;
    for ( id in this.others ) {
        if ( this.others[ id ] + 23000 < now ) {
            delete this.others[ id ];
        } else if ( id < this.id ) {
            takeMaster = false;
        }
    }
    if ( this.isMaster !== takeMaster ) {
        this.isMaster = takeMaster;
        this.masterDidChange( takeMaster );
    }
};

Dispatcher.prototype.masterDidChange = function () {};

Dispatcher.prototype.broadcast = function ( type, data ) {
    var event = {
        id: this.id,
        type: type
    };
    for ( var x in data ) {
        event[x] = data[x];
    }
    try {
        data = JSON.stringify( event );
        localStorage.setItem( this.channel_name, data );
        if (this.broadcast_to_self) this.callbacks[ type ].call( this, JSON.parse(data) );
    } catch ( error ) {}
};

Dispatcher.prototype.on = function (event_name, callback) {
    this.callbacks[event_name] = callback;
    return this;
}

Dispatcher.prototype.off = function (event_name) {
    delete this.callbacks[event_name];
}