LayerGroup.js

/*
 * L.LayerGroup is a class to combine several layers so you can manipulate the group (e.g. add/remove it) as one layer.
 */

L.LayerGroup = L.Class.extend({
	initialize: function (layers) {
		this._layers = {};

		var i, len;

		if (layers) {
			for (i = 0, len = layers.length; i < len; i++) {
				this.addLayer(layers[i]);
			}
		}
	},

	addLayer: function (layer) {
		var id = L.Util.stamp(layer);

		this._layers[id] = layer;

		if (this._map) {
			this._map.addLayer(layer);
		}

		return this;
	},

	removeLayer: function (layer) {
		var id = L.Util.stamp(layer);

		delete this._layers[id];

		if (this._map) {
			this._map.removeLayer(layer);
		}

		return this;
	},

	clearLayers: function () {
		this.eachLayer(this.removeLayer, this);
		return this;
	},

	invoke: function (methodName) {
		var args = Array.prototype.slice.call(arguments, 1),
			i, layer;

		for (i in this._layers) {
			if (this._layers.hasOwnProperty(i)) {
				layer = this._layers[i];

				if (layer[methodName]) {
					layer[methodName].apply(layer, args);
				}
			}
		}

		return this;
	},

	onAdd: function (map) {
		this._map = map;
		this.eachLayer(map.addLayer, map);
	},

	onRemove: function (map) {
		this.eachLayer(map.removeLayer, map);
		this._map = null;
	},

	addTo: function (map) {
		map.addLayer(this);
		return this;
	},

	eachLayer: function (method, context) {
		for (var i in this._layers) {
			if (this._layers.hasOwnProperty(i)) {
				method.call(context, this._layers[i]);
			}
		}
	}
});

L.layerGroup = function (layers) {
	return new L.LayerGroup(layers);
};