I'm having a hard time understanding how to map an event to a component, can someone please help me?

input(type=InputType.checkBox)

onChangeFunction = {
    console.log(it.target.asDynamic().checked) // prints "true" 
        setState {
            showOnlyPendingChanges = !it.target.asDynamic().checked // TypeError: Cannot read property 'checked' of null
        }
}