diff --git a/customelementconstructor.go b/customelementconstructor.go
index c47c14f..8b0b5fc 100644
--- a/customelementconstructor.go
+++ b/customelementconstructor.go
@@ -4,7 +4,7 @@ package dom
 
 import "syscall/js"
 
-type CustomElementConstructorCallback func() Value
+type CustomElementConstructorCallback func()
 type CustomElementConstructor struct {
 	Callback
 }
diff --git a/eventhandler.go b/eventhandler.go
index 36c2c80..94db09d 100644
--- a/eventhandler.go
+++ b/eventhandler.go
@@ -9,3 +9,6 @@ type EventHandler EventHandlerNonNull
 func JSValueToEventHandler(val js.Value) EventHandler {
 	return EventHandler(JSValueToEventHandlerNonNull(val))
 }
+func NewEventHandler(c EventHandlerNonNullCallback) EventHandler {
+	return EventHandler(NewEventHandlerNonNull(c))
+}
diff --git a/eventhandlernonnull.go b/eventhandlernonnull.go
index 04d8832..284ac58 100644
--- a/eventhandlernonnull.go
+++ b/eventhandlernonnull.go
@@ -4,7 +4,7 @@ package dom
 
 import "syscall/js"
 
-type EventHandlerNonNullCallback func(event Event) Value
+type EventHandlerNonNullCallback func(event Event)
 type EventHandlerNonNull struct {
 	Callback
 }
diff --git a/generate/generator.go b/generate/generator.go
index 68d84b1..c339552 100644
--- a/generate/generator.go
+++ b/generate/generator.go
@@ -307,7 +307,7 @@ func (g *Generator) generateCallback(spec Spec) (err error) {
 		args += fmt.Sprintf("%s %s", a.Name, t)
 		params += a.Name
 	}
-	b.WriteF("type %sCallback func(%s) %s", spec.Name, args, convertIDLType(spec.IDLType))
+	b.WriteF("type %sCallback func(%s)", spec.Name, args)
 
 	b.WriteF("type %s struct {", spec.Name)
 	b.WriteString("Callback")
@@ -378,6 +378,13 @@ func (g *Generator) generateTypedef(spec Spec) (err error) {
 	}
 	b.WriteString("}")
 
+	p, ok := g.specs[t]
+	if ok && p.Type == "callback" {
+		b.WriteF("func New%s(c %sCallback) %s {", spec.Name, p.Name, spec.Name)
+		b.WriteF("return %s(New%s(c))", spec.Name, p.Name)
+		b.WriteString("}")
+	}
+
 	return g.writeFile(spec, b)
 }
 
diff --git a/onbeforeunloadeventhandler.go b/onbeforeunloadeventhandler.go
index 229e65d..7f5611e 100644
--- a/onbeforeunloadeventhandler.go
+++ b/onbeforeunloadeventhandler.go
@@ -9,3 +9,6 @@ type OnBeforeUnloadEventHandler OnBeforeUnloadEventHandlerNonNull
 func JSValueToOnBeforeUnloadEventHandler(val js.Value) OnBeforeUnloadEventHandler {
 	return OnBeforeUnloadEventHandler(JSValueToOnBeforeUnloadEventHandlerNonNull(val))
 }
+func NewOnBeforeUnloadEventHandler(c OnBeforeUnloadEventHandlerNonNullCallback) OnBeforeUnloadEventHandler {
+	return OnBeforeUnloadEventHandler(NewOnBeforeUnloadEventHandlerNonNull(c))
+}
diff --git a/onbeforeunloadeventhandlernonnull.go b/onbeforeunloadeventhandlernonnull.go
index 52ceca3..f268e6a 100644
--- a/onbeforeunloadeventhandlernonnull.go
+++ b/onbeforeunloadeventhandlernonnull.go
@@ -4,7 +4,7 @@ package dom
 
 import "syscall/js"
 
-type OnBeforeUnloadEventHandlerNonNullCallback func(event Event) string
+type OnBeforeUnloadEventHandlerNonNullCallback func(event Event)
 type OnBeforeUnloadEventHandlerNonNull struct {
 	Callback
 }
diff --git a/onerroreventhandler.go b/onerroreventhandler.go
index 8ca1469..9caec81 100644
--- a/onerroreventhandler.go
+++ b/onerroreventhandler.go
@@ -9,3 +9,6 @@ type OnErrorEventHandler OnErrorEventHandlerNonNull
 func JSValueToOnErrorEventHandler(val js.Value) OnErrorEventHandler {
 	return OnErrorEventHandler(JSValueToOnErrorEventHandlerNonNull(val))
 }
+func NewOnErrorEventHandler(c OnErrorEventHandlerNonNullCallback) OnErrorEventHandler {
+	return OnErrorEventHandler(NewOnErrorEventHandlerNonNull(c))
+}
diff --git a/onerroreventhandlernonnull.go b/onerroreventhandlernonnull.go
index 010229e..38a1a8e 100644
--- a/onerroreventhandlernonnull.go
+++ b/onerroreventhandlernonnull.go
@@ -4,7 +4,7 @@ package dom
 
 import "syscall/js"
 
-type OnErrorEventHandlerNonNullCallback func(event Value, source string, lineno int, colno int, error Value) Value
+type OnErrorEventHandlerNonNullCallback func(event Value, source string, lineno int, colno int, error Value)
 type OnErrorEventHandlerNonNull struct {
 	Callback
 }