how to pass data with marker in leaflet js

It sounds like you would like to add new functionality (functions, properties, etc) to an existing class. It would make sense to use object-oriented principals for this. For this purpose, I’d recommend you extending the CircleMarker class to add those properties.

customCircleMarker = L.CircleMarker.extend({
   options: { 
      someCustomProperty: 'Custom data!',
      anotherCustomProperty: 'More data!'
   }
});

Now when you create your circle marker, create an instance of your extended object instead.

var myMarker = new customCircleMarker(myPoint, { 
    title: 'unselected',
    radius: 20,
    someCustomProperty: 'Adding custom data to this marker!',
    anotherCustomProperty: 'More custom data to this marker!'
});
myMarker.addTo(map);

Now you can get the properties like you would any other option from the marker. This is just a simple case of extending, and you can do more as needed, such as adding other properties or functions to the object.

JSFiddle example: JSFiddle