ajax authenticity_token

$.ajax({    
    type: 'POST',
    url: "<%= someregistration_path %>",
    data: { "firstname": "text_data_1", "last_name": "text_data2", "authenticity_token": "<%= form_authenticity_token %>" },                                                                                 
    error: function( xhr ){
      alert("ERROR ON SUBMIT");
    },
    success: function( data ){
      //data response can contain what we want here...
      console.log("SUCCESS, data="+data);
    }
});