Conflicting error message on compiling javascript functions

qml compiler gives conflicting errors with regards to compiling javascript functions. See these three cases:

property var loadCustom : function(data)
   

{              }

// gives warning: Could not compile binding for loadCustom: Functions without type annotations won't be compiled [compiler]

    property var loadCustom : function(data:var)
    {              }

//gives error: Type annotations are not permitted in function parameters in JavaScript functions

property var loadCustom : function(data):void
   

{              }

//gives error: Type annotations are not permitted for the return value of JavaScript functions