From 8ad890cfa69f105549d42fe43e2c016e231ddc9a Mon Sep 17 00:00:00 2001
From: Andreas Kling <kling@serenityos.org>
Date: Thu, 2 Apr 2020 09:54:15 +0200
Subject: [PATCH] js: Handle exceptions thrown during REPL execution

We now print thrown exceptions and clear the interpreter state so it
can continue running instead of refusing to do anything after an
exception has been thrown.

Fixes #1572.
---
 Userland/js.cpp | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/Userland/js.cpp b/Userland/js.cpp
index bfe9309a15..86467cd9d8 100644
--- a/Userland/js.cpp
+++ b/Userland/js.cpp
@@ -34,6 +34,7 @@
 #include <LibJS/Parser.h>
 #include <LibJS/Runtime/Array.h>
 #include <LibJS/Runtime/Date.h>
+#include <LibJS/Runtime/Error.h>
 #include <LibJS/Runtime/Function.h>
 #include <LibJS/Runtime/GlobalObject.h>
 #include <LibJS/Runtime/Object.h>
@@ -132,6 +133,12 @@ static void print_date(const JS::Object& date, HashTable<JS::Object*>&)
     printf("\033[34;1mDate %s\033[0m", static_cast<const JS::Date&>(date).string().characters());
 }
 
+static void print_error(const JS::Object& object, HashTable<JS::Object*>&)
+{
+    auto& error = static_cast<const JS::Error&>(object);
+    printf("\033[34;1m[%s]\033[0m: %s", error.name().characters(), error.message().characters());
+}
+
 void print_value(JS::Value value, HashTable<JS::Object*>& seen_objects)
 {
     if (value.is_object()) {
@@ -153,6 +160,8 @@ void print_value(JS::Value value, HashTable<JS::Object*>& seen_objects)
             return print_function(object, seen_objects);
         if (object.is_date())
             return print_date(object, seen_objects);
+        if (object.is_error())
+            return print_error(object, seen_objects);
         return print_object(object, seen_objects);
     }
 
@@ -268,7 +277,13 @@ void repl(JS::Interpreter& interpreter)
             program->dump(0);
 
         auto result = interpreter.run(*program);
-        print(result);
+        if (interpreter.exception()) {
+            printf("Exception caught: ");
+            print(interpreter.exception()->value());
+            interpreter.clear_exception();
+        } else {
+            print(result);
+        }
     }
 }