postDraw sample

www/js/graph.js

@@ -47,14 +47,14 @@ class Graph {
     }
 
     draw() {
-        this.preDraw();
+        this.ctx.clearRect(0, 0, this.canvas.width, this.canvas.height);
+
+        this.preDraw(this);
         this._draw();
-        this.postDraw();
+        this.postDraw(this);
     }
 
     _draw() {
-        this.ctx.clearRect(0, 0, this.canvas.width, this.canvas.height);
-
         this.ctx.beginPath();
         this.ctx.moveTo(0, 0);
 
@@ -86,7 +86,7 @@ class Graph {
         this.ctx.fill();
     }
 
-    _dummyFunc() {}
+    _dummyFunc(_) {}
 }
 
 class MovingGraph extends Graph {

www/main.html

@@ -154,6 +154,8 @@
                 
                 graph.smooth = true; // Can change on fly
 
+                graph.postDraw = postDraw;
+
                 let amount = Math.random() * graph.getLength() * 1.4;
                 for (let v = 0; v < amount; v++) {
                     graph.add( Math.random() * 100 );
@@ -178,6 +180,15 @@
                 }
             }
 
+            function postDraw(graph) {
+                graph.ctx.beginPath();
+                
+                graph.ctx.moveTo(0, 100);
+                graph.ctx.lineTo(10000, 100);
+
+                graph.ctx.stroke();
+            }
+
             function callbackData(data) {
                 console.log(data);
             }