postal.js/src/ChannelDefinition.js

var ChannelDefinition = function ( channelName, defaultTopic ) {
	this.channel = channelName || DEFAULT_CHANNEL;
	this._topic = defaultTopic || "";
};

ChannelDefinition.prototype = {
	subscribe : function () {
		var len = arguments.length;
		if ( len === 1 ) {
			return new SubscriptionDefinition( this.channel, this._topic, arguments[0] );
		}
		else if ( len === 2 ) {
			return new SubscriptionDefinition( this.channel, arguments[0], arguments[1] );
		}
	},

	publish : function ( obj ) {
		var _obj = obj || {};
		var envelope = {
			channel : this.channel,
			topic : this._topic,
			data : _obj
		};
		// If this is an envelope....
		if ( _obj.topic && _obj.data ) {
			envelope = _obj;
			envelope.channel = envelope.channel || this.channel;
		}
		envelope.timeStamp = new Date();
		postal.configuration.bus.publish( envelope );
		return envelope;
	},

	topic : function ( topic ) {
		if ( topic === this._topic ) {
			return this;
		}
		return new ChannelDefinition( this.channel, topic );
	}
};