Make paths insensitive to the order of its map's moveend handlers (#4855)

* Make Paths always update after renderer updates

Close #4851

* Add test

* Add docs for update event

* Remove listener when layer is removed

spec/suites/layer/vector/PathSpec.js

@@ -52,5 +52,30 @@ describe('Path', function () {
 			expect(mapSpy.called).to.be.ok();
 		});
 
+		it('can add a layer while being inside a moveend handler', function (done) {
+			var zoneLayer = L.layerGroup();
+			var polygon;
+			map.addLayer(zoneLayer);
+
+			map.on('moveend', function () {
+				zoneLayer.clearLayers();
+				polygon = new L.Polygon([[1, 2], [3, 4], [5, 6]]);
+				zoneLayer.addLayer(polygon);
+			});
+
+			map.invalidateSize();
+			map.setView([1, 2], 12, {animate: false});
+
+			map.panBy([-260, 0]);
+			setTimeout(function () {
+				expect(polygon._parts.length).to.be(0);
+				map.panBy([260, 0]);
+				setTimeout(function () {
+					expect(polygon._parts.length).to.be(1);
+					done();
+				}, 300);
+			}, 300);
+		});
+
 	});
 });

src/layer/vector/Path.js

@@ -76,16 +76,17 @@ L.Path = L.Layer.extend({
 		this._renderer._initPath(this);
 		this._reset();
 		this._renderer._addPath(this);
+		this._renderer.on('update', this._update, this);
 	},
 
 	onRemove: function () {
 		this._renderer._removePath(this);
+		this._renderer.off('update', this._update, this);
 	},
 
 	getEvents: function () {
 		return {
 			zoomend: this._project,
-			moveend: this._update,
 			viewreset: this._reset
 		};
 	},

src/layer/vector/Renderer.js

@@ -13,6 +13,9 @@
  *
  * Do not use this class directly, use `SVG` and `Canvas` instead.
  *
+ * @event update: Event
+ * Fired when the renderer updates its bounds, center and zoom, for example when
+ * its map has moved
  */
 
 L.Renderer = L.Layer.extend({
@@ -100,6 +103,8 @@ L.Renderer = L.Layer.extend({
 
 		this._center = this._map.getCenter();
 		this._zoom = this._map.getZoom();
+
+		this.fire('update');
 	}
 });