Added error handler for dealing with loading user js code

v2/internal/ffenestri/ffenestri_darwin.c

@@ -140,6 +140,16 @@ void Debug(struct Application *app, const char *message, ... ) {
 	}
 }
 
+void Error(struct Application *app, const char *message, ... ) {
+    const char *temp = concat("LEFfenestri (C) | ", message);
+    va_list args;
+    va_start(args, message);
+    vsnprintf(logbuffer, MAXMESSAGE, temp, args);
+    app->sendMessageToBackend(&logbuffer[0]);
+    MEMFREE(temp);
+    va_end(args);
+}
+
 void Fatal(struct Application *app, const char *message, ... ) {
   const char *temp = concat("LFFfenestri (C) | ", message);
   va_list args;
@@ -246,7 +256,10 @@ void messageHandler(id self, SEL cmd, id contentController, id message) {
 	struct Application *app = (struct Application *)objc_getAssociatedObject(
 							  self, "application");
 	const char *name = (const char *)msg(msg(message, s("name")), s("UTF8String"));
-	if( strcmp(name, "completed") == 0) {
+	if( strcmp(name, "error") == 0 ) {
+	    printf("There was a Javascript error. Please open the devtools for more information.\n");
+	    Show(app);
+	} else if( strcmp(name, "completed") == 0) {
 		// Delete handler
 		msg(app->manager, s("removeScriptMessageHandlerForName:"), str("completed"));
 
@@ -450,6 +463,7 @@ void DestroyApplication(struct Application *app) {
 	msg(app->manager, s("removeScriptMessageHandlerForName:"), str("contextMenu"));
 	msg(app->manager, s("removeScriptMessageHandlerForName:"), str("windowDrag"));
 	msg(app->manager, s("removeScriptMessageHandlerForName:"), str("external"));
+	msg(app->manager, s("removeScriptMessageHandlerForName:"), str("error"));
 
 	// Close main window
 	msg(app->mainWindow, s("close"));
@@ -1534,6 +1548,7 @@ void Run(struct Application *app, int argc, char **argv) {
 	id manager = msg(config, s("userContentController"));
 	msg(manager, s("addScriptMessageHandler:name:"), app->delegate, str("external"));
 	msg(manager, s("addScriptMessageHandler:name:"), app->delegate, str("completed"));
+	msg(manager, s("addScriptMessageHandler:name:"), app->delegate, str("error"));
 	app->manager = manager;
 
 	id wkwebview = msg(c("WKWebView"), s("alloc"));

v2/internal/runtime/js/core/desktop.js

@@ -10,6 +10,7 @@ The lightweight framework for web-like apps
 /* jshint esversion: 6 */
 import { SetBindings } from './bindings';
 import { Init } from './main';
+import {RaiseError} from '../desktop/darwin';
 
 // Setup global error handler
 window.onerror = function (msg, url, lineNo, columnNo, error) {
@@ -21,7 +22,7 @@ window.onerror = function (msg, url, lineNo, columnNo, error) {
 		error: JSON.stringify(error),
 		stack: function() { return JSON.stringify(new Error().stack); }(),
 	};
-	window.wails.Log.Error(JSON.stringify(errorMessage));
+	RaiseError(errorMessage);
 };
 
 // Initialise the Runtime

v2/internal/runtime/js/desktop/darwin.js

@@ -25,6 +25,10 @@ export function SendMessage(message) {
     window.webkit.messageHandlers.external.postMessage(message);
 }
 
+export function RaiseError(message) {
+    window.webkit.messageHandlers.error.postMessage(message);
+}
+
 export function Init() {
 
     // Setup drag handler

v2/internal/runtime/js/webpack.desktop.js

@@ -13,7 +13,7 @@ module.exports = {
   mode: 'production',
   output: {
     path: path.resolve(__dirname, '..', 'assets'),
-    filename: 'desktop.js',
+    filename: 'desktop_'+platform+'.js',
     library: 'Wails'
   },
   resolve: {

v2/internal/runtime/scripts/rebuild.go

@@ -3,12 +3,13 @@ package main
 import (
 	"bytes"
 	"fmt"
-	"github.com/wailsapp/wails/v2/internal/fs"
-	"github.com/wailsapp/wails/v2/internal/shell"
 	"io/ioutil"
 	"log"
 	"os"
 	"strings"
+
+	"github.com/wailsapp/wails/v2/internal/fs"
+	"github.com/wailsapp/wails/v2/internal/shell"
 )
 
 func main() {
@@ -49,7 +50,7 @@ func main() {
 			log.Fatal(err)
 		}
 
-		wailsJS := fs.RelativePath("../../../internal/runtime/assets/desktop.js")
+		wailsJS := fs.RelativePath("../../../internal/runtime/assets/desktop_" + platform + ".js")
 		runtimeData, err := ioutil.ReadFile(wailsJS)
 		if err != nil {
 			log.Fatal(err)