defining statics function (like in mongoose) in mySql using sequelize

Trying to define a function inside the model so that I can have a common set of functions.Here is my code for my table. I am using sequelize ORM and nodejs

"use strict";

module.exports = function(sequelize, DataTypes) {
  var AttendantUser = sequelize.define('AttendantUser', {
    user_id : {
      type : DataTypes.CHAR(36),
      defaultValue : DataTypes.UUIDV4,
      primaryKey : true
    },
    mobile : {
        type : DataTypes.BIGINT,
        allowNull : false,
        unique : true
    },
    reset_code : {
      type : DataTypes.INTEGER,
      allowNull : true,
      defaultValue : '0000'
    }
  },{
    freezeTableName : true,
    paranoid : true
  });


AttendantUser.usernameInUse = function (callback) {
 console.log("fefe");
 callback(null, "hello");
 }
  return AttendantUser;
};

The error I get when I try to use usernameInUse function is . error: mModels.usernameInUse is not a function

via sac Dahal