Fix CanvasFrame loadFromURL

lib/CanvasFrame.js

@@ -30,15 +30,13 @@ class CanvasFrame {
         this.canvas.height = h;
         this.ctx = this.canvas.getContext('2d')
     }
-    replace(layer) {
-        this.canvas
-    }
     async loadFromURL(url) {
         let img = new Image()
         img.src = url;
         await new Promise((resolve, reject) => {
-            img.onload = function() {
-                resolve()
+            img.onload = () => {
+                this.loadFromImage(img);
+                resolve();
             }
             img.onerror = reject;
         })