Log errors in __DEV__ mode (Fix #905)

src/Logger.js

@@ -17,4 +17,14 @@ export default class Logger {
                 [Date.now() - this.start + 'ms', 'html2canvas:'].concat([].slice.call(args, 0))
             );
     }
+
+    // eslint-disable-next-line flowtype/no-weak-types
+    error(...args: any) {
+        Function.prototype.bind
+            .call(window.console.error, window.console)
+            .apply(
+                window.console,
+                [Date.now() - this.start + 'ms', 'html2canvas:'].concat([].slice.call(args, 0))
+            );
+    }
 }

src/index.js

@@ -51,7 +51,7 @@ const html2canvas = (element: HTMLElement, config: Options): Promise<HTMLCanvasE
         return Promise.reject(__DEV__ ? `Invalid canvas element provided in options` : '');
     }
 
-    return cloneWindow(
+    const result = cloneWindow(
         ownerDocument,
         ownerDocument,
         windowBounds,
@@ -102,6 +102,14 @@ const html2canvas = (element: HTMLElement, config: Options): Promise<HTMLCanvasE
             return renderer.render(stack);
         });
     });
+
+    if (__DEV__) {
+        return result.catch(e => {
+            logger.error(e);
+            throw e;
+        });
+    }
+    return result;
 };
 
 module.exports = html2canvas;