extend cc.MenuItemSprite is not working!

try {

var CoreCustomButton = cc.MenuItemSprite.extend({
m_JsonValue:null,

ctor:function() {
this.*super;
cc.log;
},
selected:function {
this.*super();
},

unselected:function() {
this._super();
},

setJsonValue:function( value ){
this.m_JsonValue = value;
},

getJsonValue:function() {
return m_JsonValue;
},
});

CoreCustomButton.create = function( normalImage, selectedImage, disabledImage, selector, target ){
var pRet = new CoreCustomButton();

cc.log( “CoreCustomButton new after” );
if( pRet.initWithNormalSprite( normalImage, selectedImage, disabledImage, selector, target ) ){
return pRet;
}

delete pRet;
return null;
};

} catch(e) {log(e);}

err message!
CoreCustomButton.js:32:TypeError: pRet.initWithNormalSprite is not a function