Adds 'throw' method to val. (emscripten-core#7405)

As mentioned in emscripten-core#6330.
Something like this will now work:

val::global("TypeError").new_("wrong type").throw_();

In the tests found in test_val.cpp it can be seen that an error can be thrown in CPP and successfully caught in JS.

Author: robfors

src/embind/emval.js

@@ -453,6 +453,12 @@ var LibraryEmVal = {
     return delete object[property];
   },
 
+  _emval_throw__deps: ['$requireHandle'],
+  _emval_throw: function(object) {
+    object = requireHandle(object);
+    throw object;
+  },
+
 };
 
 mergeInto(LibraryManager.library, LibraryEmVal);

system/include/emscripten/val.h

@@ -97,6 +97,7 @@ namespace emscripten {
             bool _emval_instanceof(EM_VAL object, EM_VAL constructor);
             bool _emval_in(EM_VAL item, EM_VAL object);
             bool _emval_delete(EM_VAL object, EM_VAL property);
+            bool _emval_throw(EM_VAL object);
         }
 
         template<const char* address>
@@ -511,6 +512,10 @@ namespace emscripten {
             return internal::_emval_delete(handle, val(property).handle);
         }
 
+        void throw_() const {
+            internal::_emval_throw(handle);
+        }
+
     private:
         // takes ownership, assumes handle already incref'd
         explicit val(internal::EM_VAL handle)

tests/embind/test_val.cpp

@@ -57,6 +57,16 @@ void ensure_js_not(string js_code)
   ensure_js(js_code);
 }
 
+void throw_js_error(val js_error)
+{
+  js_error.throw_();
+}
+
+EMSCRIPTEN_BINDINGS(test_bindings)
+{
+  emscripten::function("throw_js_error", &throw_js_error);
+}
+
 int main()
 {
   printf("start\n");
@@ -512,6 +522,29 @@ int main()
   ensure_js_not("1 in a");
   ensure_js_not("'c' in a");
 
+  test("void throw_() const");
+  EM_ASM(
+    test_val_throw_ = function(error)
+    {
+      try
+      {
+        Module.throw_js_error(error);
+        return false;
+      }
+      catch(error_thrown)
+      {
+        if (error_thrown != error)
+          throw error_thrown;
+      }
+      return true;
+    }
+  );
+  ensure_js("test_val_throw_(new Error)");
+  ensure_js("test_val_throw_(Error)");
+  ensure_js("test_val_throw_(2)");
+  ensure_js("test_val_throw_('message')");
+  ensure_js("test_val_throw_(new TypeError('message'))");
+  
   // this test should probably go elsewhere as it is not a member of val
   test("template<typename T> std::vector<T> vecFromJSArray(val v)");
   EM_ASM(

tests/embind/test_val.out

@@ -224,6 +224,13 @@ pass
 pass
 pass
 test:
+void throw_() const
+pass
+pass
+pass
+pass
+pass
+test:
 template<typename T> std::vector<T> vecFromJSArray(val v)
 pass
 pass